[Assessment of the efficacy and safety of alemtuzumab in patients with highly active relapsing-remitting multiple sclerosis in Russian population]

OBJECTIVE

To evaluate the severity and frequency of infusion reactions (IR) in patients with highly active relapsing-remitting multiple sclerosis (MS) In Russian population receiving alemtuzumab therapy.

MATERIAL AND METHODS

In retrospective study, we analyzed data from 50 patients with highly active relapsing-remitting multiple sclerosis (MS) from six Regional MS Centers in the Russian Federation who received two courses of alemtuzumab between 2018 and 2022.

RESULTS

Among all IRs, the most frequently reported were hives-like rashes, which were registered in 27 people, mostly of mild severity (70.6%). Headaches were the second most common IR, observed in 17 patients (34%). When comparing the group of patients who underwent music therapy (MT) with those who received alemtuzumab therapy without MT, no statistically significant difference was found in the frequency and severity of IRs.

CONCLUSION

All patients experienced IRs of varying degrees of severity. A decrease in the score on the EDSS disability scale was noted. MT did not affect the occurrence or severity of IRs.

[Epidemiology of neuromyelitis optica spectrum disorder]

Neuromyelitis optica spectrum disorder (NMOSD) is a group of rare and mostly severe autoimmune demyelinating central nervous system disorders which prevalence is 0.7-1 per 100.000 population and incidence is 0.037-0.73 per 100.000 person-years. NMOSD may present as a combination of uni- or bilateral optic neuritis, transverse myelitis or lesions of brain stem and other brain regions. The symptoms are mostly relapsing (up to 97.5%) and progressive. Occurrence of relapses is associated with seropositivity for aquaporin-4 (up to 80% of NMOSD patients) and bears a less favorable prognosis (mortality up to 32%). Women seropositive for aquaporin 4 constitute 90% of NMOSD patients. Compared to other demyelinating disorders, NMOSD is characterized by late onset (mean age is about 39 years) and association with other autoimmune disorders, including systemic lupus erythematosus, myasthenia gravis and Sjogren's syndrome. A genetic predisposition was found among Blacks and Asians, with HLA-DRB1*03:01 gene associated with higher risk of NMOSD in Asians. The course of the disease tends to be more severe in Blacks. There are clusters of an increased incidence of NMOSD in the Carribeans and in the Far East. Continued increase of prevalence and incidence of NMOSD worldwide compels continued epidemiological research in order to provide early diagnosis and treatment for this disorder.

[Efficacy, tolerability and safety of the treatment with teberif: the results of a 2-year randomized clinical trial of treatment naïve patients with remitting multiple sclerosis, who have not received DMT, after switching from other interferon β-1a]

OBJECTIVES

To evaluate efficacy, safety, and tolerability of the treatment with teberif/interferon β-1a, to analyze safety, tolerability and dynamics of key efficacy variables after switching from referent drug rebif to biosimilar teberif in patients with remitting multiple sclerosis (RMS).

MATERIAL AND METHODS

During the main period of the international multicenter randomized study patients were randomized to receive treatment with teberif for 52 weeks, or rebif for 52 weeks, or placebo for 16 weeks to evaluate efficacy and safety of treatment. After the main study period, patients were group-independently switched to take open-label teberif treatment during the next 48 weeks.

RESULTS AND CONCLUSION

The analysis of multiple evaluation parameters of the efficiency during the 1st study period (blinded) and the 2^nd study period (open-label) has shown that teberif and rebif demonstrate equivalent efficacy and stable 2-year efficacy of teberif was proven. There were no significant differences between teberif and rebif for all safety, and tolerability parameters. Switching from rebif to teberif didn't influence treatment efficacy. The 2-year study results confirmed a biosimilar teberif's benign tolerability and expected safety profile to other interferons β-1a in patients with RMS.

OpenSim: Simulating musculoskeletal dynamics and neuromuscular control to study human and animal movement

Movement is fundamental to human and animal life, emerging through interaction of complex neural, muscular, and skeletal systems. Study of movement draws from and contributes to diverse fields, including biology, neuroscience, mechanics, and robotics. OpenSim unites methods from these fields to create fast and accurate simulations of movement, enabling two fundamental tasks. First, the software can calculate variables that are difficult to measure experimentally, such as the forces generated by muscles and the stretch and recoil of tendons during movement. Second, OpenSim can predict novel movements from models of motor control, such as kinematic adaptations of human gait during loaded or inclined walking. Changes in musculoskeletal dynamics following surgery or due to human-device interaction can also be simulated; these simulations have played a vital role in several applications, including the design of implantable mechanical devices to improve human grasping in individuals with paralysis. OpenSim is an extensible and user-friendly software package built on decades of knowledge about computational modeling and simulation of biomechanical systems. OpenSim's design enables computational scientists to create new state-of-the-art software tools and empowers others to use these tools in research and clinical applications. OpenSim supports a large and growing community of biomechanics and rehabilitation researchers, facilitating exchange of models and simulations for reproducing and extending discoveries. Examples, tutorials, documentation, and an active user forum support this community. The OpenSim software is covered by the Apache License 2.0, which permits its use for any purpose including both nonprofit and commercial applications. The source code is freely and anonymously accessible on GitHub, where the community is welcomed to make contributions. Platform-specific installers of OpenSim include a GUI and are available on simtk.org.

[A comparative placebo-controlled clinical study on the efficacy and safety of interferon beta-1a for subcutaneous injections in patients with remitting multiple sclerosis: results of the first year of observations]

AIM

To prove the equivalent efficacy of teberif (BCD-033, interferon beta-1) and rebif (interferon beta-1a) in patients with remitting multiple sclerosis (RMS).

MATERIAL AND METHODS

A multicenter double blind placebo-controlled comparative randomized III phase study included 163 patients with RMS. Patients were randomized into three equal groups (teberif, rebif or placebo).

RESULTS AND CONCLUSION

After 52 weeks, the equivalent efficacy of teberif and the brand drug rebif was shown. The result of assessment of the primary endpoint, which was combined unique active (CUA) lesion (the total of MRI T1-weighted lesions and new or newly enlarging T2-weighted lesions, without double counting of lesions with both activities), showed no significant differences (0.727±1.042 and 0.652±1.059 (p=0.7354, t-Student test) in the teberif and rebif groups, respectively. No between-group differences were found for other MRI indices and clinical parameters related with relapses. Teberif was shown to have a favorable safety and tolerability profile comparable to that of rebif. The results suggest the therapeutic equivalency of the drugs and form the basis for using the bioanalogue of interferon-beta 1 in patients with RMS.

[Clinical and morphologic efficacy of a complex antioxidant and energy correction therapy of different duration in brain infarction: results of a multicenter randomized trial]

AIM

To compare clinical and morphological results of treatment of ischemic stroke in three groups of patients which differed by the forms and duration of an antioxidant therapy.

MATERIAL AND METHODS

A randomized clinical trial was performed in 8 vascular centers of the Russian Federation in 2010-2014. It included 373 patients with ischemic stroke in the carotid territory. Patients were randomized into 3 groups to receive different regimens of antioxidant therapy as an adjunct to standard therapy: control group (ascorbic acid; 132 patients); cytoflavin (20 ml per day for 10 days; 133 patients); cytoflavin (the dose was decreased to 10 ml per day from 11th to 20th day) (108 patients). Patient's condition was assessed in 1, 10 and 21 day by a complex of clinical, laboratory and instrumental methods.

RESULTS AND CONCLUSION

The analysis of CT in 1th and 21th day revealed a significant 1,5-1,7- fold decrease in the cerebral ischemic lesion in both groups treated with cytoflavin with no significant morphologic changes in the ascorbic acid group. The percentage of patients with ischemic lesion, increased during days 1-21, was 2-fold higher in the ascorbic acid group compared to cytoflavin groups. Morphologic changes were correlated with clinical variables and outcome. In patients with ≥14 points on NIH scale on admission, prolonged 20 day cytoflavin therapy was associated with a more prominent improvement of neurologic, functional and cognitive status compared to 10-day cytoflavin infusion. No differences in clinical variables were observed in patients with mild symptoms (<14 points on NIH scale on admission) receiving cytoflavin for 10 and 20 days.

Making a meaningful impact: modelling simultaneous frictional collisions in spatial multibody systems

Impacts are instantaneous, computationally efficient approximations of collisions. Current impact models sacrifice important physical principles to achieve that efficiency, yielding qualitative and quantitative errors when applied to simultaneous impacts in spatial multibody systems. We present a new impact model that produces behaviour similar to that of a detailed compliant contact model, while retaining the efficiency of an instantaneous method. In our model, time and configuration are fixed, but the impact is resolved into distinct compression and expansion phases, themselves comprising sliding and rolling intervals. A constrained optimization problem is solved for each interval to compute incremental impulses while respecting physical laws and principles of contact mechanics. We present the mathematical model, algorithms for its practical implementation, and examples that demonstrate its effectiveness. In collisions involving materials of various stiffnesses, our model can be more than 20 times faster than integrating through the collision using a compliant contact model. This work extends the use of instantaneous impact models to scientific and engineering applications with strict accuracy requirements, where compliant contact models would otherwise be required. An open-source implementation is available in Simbody, a C++ multibody dynamics library widely used in biomechanical and robotic applications.

WHAT IS A MOMENT ARM? CALCULATING MUSCLE EFFECTIVENESS IN BIOMECHANICAL MODELS USING GENERALIZED COORDINATES

Biomechanics researchers often use multibody models to represent biological systems. However, the mapping from biology to mechanics and back can be problematic. OpenSim is a popular open source tool used for this purpose, mapping between biological specifications and an underlying generalized coordinate multibody system called Simbody. One quantity of interest to biomechanical researchers and clinicians is "muscle moment arm," a measure of the effectiveness of a muscle at contributing to a particular motion over a range of configurations. OpenSim can automatically calculate these quantities for any muscle once a model has been built. For simple cases, this calculation is the same as the conventional moment arm calculation in mechanical engineering. But a muscle may span several joints (e.g., wrist, neck, back) and may follow a convoluted path over various curved surfaces. A biological joint may require several bodies or even a mechanism to accurately represent in the multibody model (e.g., knee, shoulder). In these situations we need a careful definition of muscle moment arm that is analogous to the mechanical engineering concept, yet generalized to be of use to biomedical researchers. Here we present some biomechanical modeling challenges and how they are resolved in OpenSim and Simbody to yield biologically meaningful muscle moment arms.

Simbios: an NIH national center for physics-based simulation of biological structures

Physics-based simulation provides a powerful framework for understanding biological form and function. Simulations can be used by biologists to study macromolecular assemblies and by clinicians to design treatments for diseases. Simulations help biomedical researchers understand the physical constraints on biological systems as they engineer novel drugs, synthetic tissues, medical devices, and surgical interventions. Although individual biomedical investigators make outstanding contributions to physics-based simulation, the field has been fragmented. Applications are typically limited to a single physical scale, and individual investigators usually must create their own software. These conditions created a major barrier to advancing simulation capabilities. In 2004, we established a National Center for Physics-Based Simulation of Biological Structures (Simbios) to help integrate the field and accelerate biomedical research. In 6 years, Simbios has become a vibrant national center, with collaborators in 16 states and eight countries. Simbios focuses on problems at both the molecular scale and the organismal level, with a long-term goal of uniting these in accurate multiscale simulations.

Fast flexible modeling of RNA structure using internal coordinates

Modeling the structure and dynamics of large macromolecules remains a critical challenge. Molecular dynamics (MD) simulations are expensive because they model every atom independently, and are difficult to combine with experimentally derived knowledge. Assembly of molecules using fragments from libraries relies on the database of known structures and thus may not work for novel motifs. Coarse-grained modeling methods have yielded good results on large molecules but can suffer from difficulties in creating more detailed full atomic realizations. There is therefore a need for molecular modeling algorithms that remain chemically accurate and economical for large molecules, do not rely on fragment libraries, and can incorporate experimental information. RNABuilder works in the internal coordinate space of dihedral angles and thus has time requirements proportional to the number of moving parts rather than the number of atoms. It provides accurate physics-based response to applied forces, but also allows user-specified forces for incorporating experimental information. A particular strength of RNABuilder is that all Leontis-Westhof basepairs can be specified as primitives by the user to be satisfied during model construction. We apply RNABuilder to predict the structure of an RNA molecule with 160 bases from its secondary structure, as well as experimental information. Our model matches the known structure to 10.2 Angstroms RMSD and has low computational expense.

Simbody: multibody dynamics for biomedical research

Multibody software designed for mechanical engineering has been successfully employed in biomedical research for many years. For real time operation some biomedical researchers have also adapted game physics engines. However, these tools were built for other purposes and do not fully address the needs of biomedical researchers using them to analyze the dynamics of biological structures and make clinically meaningful recommendations. We are addressing this problem through the development of an open source, extensible, high performance toolkit including a multibody mechanics library aimed at the needs of biomedical researchers. The resulting code, Simbody, supports research in a variety of fields including neuromuscular, prosthetic, and biomolecular simulation, and related research such as biologically-inspired design and control of humanoid robots and avatars. Simbody is the dynamics engine behind OpenSim, a widely used biomechanics simulation application. This article reviews issues that arise uniquely in biomedical research, and reports on the architecture, theory, and computational methods Simbody uses to address them. By addressing these needs explicitly Simbody provides a better match to the needs of researchers than can be obtained by adaptation of mechanical engineering or gaming codes. Simbody is a community resource, free for any purpose. We encourage wide adoption and invite contributions to the code base at https://simtk.org/home/simbody.

The Simbios National Center: Systems Biology in Motion

Physics-based simulation is needed to understand the function of biological structures and can be applied across a wide range of scales, from molecules to organisms. Simbios (the National Center for Physics-Based Simulation of Biological Structures, http://www.simbios.stanford.edu/) is one of seven NIH-supported National Centers for Biomedical Computation. This article provides an overview of the mission and achievements of Simbios, and describes its place within systems biology. Understanding the interactions between various parts of a biological system and integrating this information to understand how biological systems function is the goal of systems biology. Many important biological systems comprise complex structural systems whose components interact through the exchange of physical forces, and whose movement and function is dictated by those forces. In particular, systems that are made of multiple identifiable components that move relative to one another in a constrained manner are multibody systems. Simbios' focus is creating methods for their simulation. Simbios is also investigating the biomechanical forces that govern fluid flow through deformable vessels, a central problem in cardiovascular dynamics. In this application, the system is governed by the interplay of classical forces, but the motion is distributed smoothly through the materials and fluids, requiring the use of continuum methods. In addition to the research aims, Simbios is working to disseminate information, software and other resources relevant to biological systems in motion.

The role of charged amphipathic helices in the structure and function of surfactant protein B

Surfactant protein B (SP-B) is essential for normal lung surfactant function. Theoretical models predict that the disulfide cross-linked, N- and C-terminal domains of SP-B fold as charged amphipathic helices, and suggest that these adjacent helices participate in critical surfactant activities. This hypothesis is tested using a disulfide-linked construct (Mini-B) based on the primary sequences of the N- and C-terminal domains. Consistent with theoretical predictions of the full-length protein, both isotope-enhanced Fourier transform infrared (FTIR) spectroscopy and molecular modeling confirm the presence of charged amphipathic alpha-helices in Mini-B. Similar to that observed with native SP-B, Mini-B in model surfactant lipid mixtures exhibits marked in vitro activity, with spread films showing near-zero minimum surface tensions during cycling using captive bubble surfactometry. In vivo, Mini-B shows oxygenation and dynamic compliance that compare favorably with that of full-length SP-B. Mini-B variants (i.e. reduced disulfides or cationic residues replaced by uncharged residues) or Mini-B fragments (i.e. unlinked N- and C-terminal domains) produced greatly attenuated in vivo and in vitro surfactant properties. Hence, the combination of structure and charge for the amphipathic alpha-helical N- and C-terminal domains are key to SP-B function.

Membrane-Bound Dimer Structure of a β-Hairpin Antimicrobial Peptide from Rotational-Echo Double-Resonance Solid-State NMR

The intermolecular packing of a beta-hairpin antimicrobial peptide, PG-1, in lipid bilayers is determined using solid-state NMR distance measurements. Previous spin counting experiments showed that PG-1 associates as dimers in POPC bilayers; however, the detailed dimer structure was unknown. We have now measured several intermolecular 13C-19F, 1H-13C, and 15N-13C distances in site-specifically labeled PG-1 to constrain the structure of the intermolecular interface. The distances are measured using the rotational-echo double-resonance (REDOR) technique under magic-angle spinning. The results indicate that two PG-1 molecules align in a parallel fashion with the C-terminal strand of the hairpin forming the dimer interface. Six hydrogen bonds stabilize this interface, and the Phe12 side chain adopts the g- conformation in the membrane as in solution. The parallel packing of the peptide in the lipid bilayer differs from the antiparallel dimer found in DPC micelles and may be stabilized by its strong amphipathic character, which should facilitate its insertion into the amphipathic lipid bilayer. This study demonstrates the utility of the REDOR NMR technique for the elucidation of the oligomeric structure of membrane proteins.

A theta-defensin composed exclusively of d-amino acids is active against HIV-1

The ability of certain theta-defensins, including retrocyclin-1, to protect human cells from infection by HIV-1 marks them as potentially useful molecules. Theta-defensins composed of L-amino acids are likely to be unstable in environments that contain host and microbial proteases. This study compared the properties of two enantiomeric theta-defensins, retrocyclin-1, and RC-112. Although these peptides have identical sequences, RC-112 is composed exclusively of D-amino acids, whereas retrocyclin-1 contains only L-amino acids. We compared the ability of these peptides to protect JC53-BL human cells from infection by 30 primary HIV-1 isolates. JC53-BL cells are modified HeLa cells that express surface CD4, CXCR4, and CCR5. They also contain reporter cassettes that are driven by the HIV-1 LTR, and express beta-galactosidase and luciferase. The HIV-1 isolates varied in co-receptor specificity and included subtypes A, B, C, D, CRF01-AE, and G. RC-112 was several fold more potent than retrocyclin-1 across the entire HIV-1 panel. Although RC-112 bound immobilized gp120 and CD4 with lower affinity than did retrocyclin-1, surface plasmon resonance experiments performed with 1 microg/mL of RC-112 and retrocyclin-1 revealed that both glycoproteins were bound to a similar extent. The superior antiviral performance of RC-112 most likely reflected its resistance to degradation by surface-associated or secreted proteases of the JC53-BL target cells. Theta-defensins composed exclusively of D-amino acids merit consideration as starting points for designing microbicides for topical application to the vagina or rectum.

[Clinical course of autonomic nervous system disorders in veterans with consequences of combat mild brain injury]

Twenty-two veterans with combat mild brain injury (BI) were studied 7 and 14.9 years after BI. Along with evaluation of clinical symptoms, the authors investigated the autonomic tonus, autonomic background, regulatory brain systems function (cardiointervalography), emotional and personality state measured by Scmiscek-Litman (MMPI-modification) and Spilberger tests. Initial examination identified clinical syndromes, such as autonomic dystonia (70% of the patients), psychopathological syndromes represented by asthenic, affective, neurotic and neurotic-like states (90%), cochleo-vestibular (30%), insomniac (20%) states. Follow-up revealed these syndromes in 100, 100, 45, 20% of the cases, respectively. There was an increase in the dysfunction of nonspecific brain systems, which emerged clinically as a psychoautonomic syndrome in the form of autonomic dystonia with an elevation of sympathetic activity and emotional shift to depressive and hypochondriac disorders.

[Function of nonspecific brain systems in mild war cranio-cerebral trauma]

129 participants of military conflicts were examined; 72 of them had a mild combat craniocerebral trauma (CCT) (8.46 +/- 0.72 years before the observation on the average); 57 hadn't any trauma; 15 healthy individuals formed a control group. The examination included an analysis of the indices of autonomic background, cardiointervalograms, EEG, EMG, visual and acoustic evoked potentials as well as peculiarities of personality according to the modified MMPI test. The results confirmed a role of chronic combat stress in the development of the dysfunction of non-specific systems of the brain in the form of psycho-autonomic syndrome, in which a main role is played by headache of tension. The development of such dysfunction did not depend on the presence of CCT while a mild CCT aggravated the severity of these cases.

Clavaspirin, an antibacterial and haemolytic peptide from Styela clava

We cloned the precursor of a novel peptide from a cDNA library prepared from pharyngeal tissues of the tunicate, Styela clava. Its sequence predicted a histidine-rich, amidated 23-residue peptide (FLRF(IG)SVIHGIGHLVHHIGVAL-NH2) that we named clavaspirin. A synthetic clavaspirin was prepared and it was found that it killed Gram-positive and Gram-negative bacteria, permeabilized the outer and inner membranes of Escherichia coli, lysed phosphatidylglycerol (POPG) liposomes, and was potently haemolytic towards human and bovine erythrocytes. Each of these activities was performed more effectively at an acidic pH. Circular dichroism measurements of synthetic clavaspirin revealed a largely alpha-helical structure and polarized and residue-specific FTIR spectrometry showed that its association with phospholipid membranes was influenced by pH. Peptides such as clavaspirin may equip tunicate haemocytes to mediate cytotoxicity and participate in antimicrobial defence.

Multimerization of a chimeric anti-CD20 single-chain Fv-Fc fusion protein is mediated through variable domain exchange

A series of single-chain anti-CD20 antibodies was produced by fusing single-chain Fv (scFv) with human IgG1 hinge and Fc regions, designated scFv-Fc. The initial scFv-Fc construct was assembled using an 18 amino acid (aa) linker between the antibody light- and heavy-chain variable regions, with the Cys residue in the upper hinge region (Kabat 233) mutagenized to Ser. Anti-CD20 scFv-Fc retained specific binding to CD20-positive cells and was active in mediating complement-dependent cytolysis. Size-exclusion HPLC analysis revealed that the purified scFv-Fc included multimeric as well as monomeric components. Variant scFv-Fcs were constructed incorporating four different hinges between the scFv and Fc regions, or three different linkers in the scFv domain. All formed multimers, with the highest level of multimerization found in the scFv-Fc with the shortest linker (8 aa). Elimination of an unusual salt bridge between residues L38 and H89 in the V(L)-V(H) domain interface failed to reduce the formation of higher order forms. Structural analysis of the scFv-Fc constructed with 18 or 8 aa linkers by pepsin or papain cleavage suggested the proteins contained a form in which scFv units had cross-paired to form a 'diabody'. Thus, domain exchange or cross-pairing appears to be the basis of the observed multimerization.

Dicynthaurin: an antimicrobial peptide from hemocytes of the solitary tunicate, Halocynthia aurantium

We isolated a novel antimicrobial peptide, dicynthaurin, from hemocytes of a tunicate, Halocynthia aurantium. The native peptide had a mass of approximately 6.2 kDa and was composed of two 30-residue monomers without sequence homology to any previously identified peptides (ILQKAVLDCLKAAGSSLSKAAITAIYNKIT). Most cynthaurin molecules were C-terminally amidated and were linked covalently by a single cystine disulfide bond. When performed in membrane-mimetic environments, circular dichroism studies of dicynthaurin revealed largely alpha-helical conformations. Dicynthaurin's broad-spectrum activity encompassed Gram-positive (Micrococcus luteus, Staphylococcus aureus, Listeria monocytogenes) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa), but not Candida albicans, a fungus. Although dicynthaurin was purified from a marine invertebrate, its antimicrobial activity was optimal at NaCl concentrations below 100 mM. This suggests that the antimicrobial actions of this molecule may take place intracellularly (e.g., within a phagosome) rather than extracellularly.

At least one class I gene in restriction fragment pattern-Y (Rfp-Y), the second MHC gene cluster in the chicken, is transcribed, polymorphic, and shows divergent specialization in antigen binding region

MHC genes in the chicken are arranged into two genetically independent clusters located on the same chromosome. These are the classical B: system and restriction fragment pattern-Y (Rfp-Y), a second cluster of MHC genes identified recently through DNA hybridization. Because small numbers of MHC class I and class II genes are present in both B: and Rfp-Y, the two clusters might be the result of duplication of an entire chromosomal segment. We subcloned, sequenced, and analyzed the expression of two class I loci mapping to Rfp-Y to determine whether Rfp-Y should be considered either as a second, classical MHC or as a region containing specialized MHC-like genes, such as class Ib genes. The Rfp-Y genes are highly similar to each other (93%) and to classical class Ia genes (73% with chicken B: class I; 49% with HLA-A). One locus is disrupted and unexpressed. The other, YFV, is widely transcribed and polymorphic. Mature YFV protein associated with beta(2)m arrives on the surface of chicken B (RP9) lymphoma cells expressing YFV as an epitope-tagged transgene. Substitutions in the YFV Ag-binding region (ABR) occur at four of the eight highly conserved residues that are essential for binding of peptide-Ag in the class Ia molecules. Therefore, it is unlikely that Ag is bound in the YFV ABR in the manner typical of class Ia molecules. This ABR specialization indicates that even though YFV is polymorphic and widely transcribed, it is, in fact, a class Ib gene, and Rfp-Y is a region containing MHC genes of specialized function.

The role of STAT6 in mast cell IL-4 production

Interleukin (IL)-4 has an important role in regulating antibody production and inflammation. The major IL-4 producers are CD4+ T cells, but the development of an IL-4-producing phenotype in these cells requires IL-4 signaling through the STAT6 pathway during differentiation. The cellular source of this early IL-4 is not known, but mast cells are a possible candidate due to their immediate and indiscriminate release of IL-4 upon activation. In this review we summarize the evidence that STAT6 signaling is not required for mast cell IL-4 production, which is consistent with their possible role as a link between the innate immune response and T-cell activation. We also describe an isoform of STAT6 that is expressed in mast cells and that appears to act as a repressor of IL-4 transcription. This STAT6 signaling pathway may be part of a feedback mechanism to protect surrounding tissues from IL-4-mediated inflammation during an infection.

Surfactant protein B and C analogues

Mammalian lung surfactant is a mixture of phospholipids and four surfactant-associated proteins (SP-A, SP-B, SP-C, and SP-D). Its major function is to reduce surface tension at the air-water interface in the terminal airways by the formation of a surface-active film highly enriched in dipalmitoyl phosphatidylcholine (DPPC), thereby preventing alveolar collapse during expiration. SP-A and SP-D are large hydrophilic proteins, which play an important role in host defense, whereas the small hydrophobic peptides SP-B and SP-C interact with DPPC to generate and maintain a surface-active film. Surfactant replacement therapy with bovine and porcine lung surfactant extracts, which contain only polar lipids and SP-B and SP-C, has revolutionized the clinical management of premature infants with respiratory distress syndrome. Newer surfactant preparations will probably be based on SP-B and SP-C, produced by recombinant technology or peptide synthesis, and reconstituted with selected synthetic lipids. The development of peptide analogues of SP-B and SP-C offers the possibility to study their molecular mechanism of action and will allow the design of surfactant formulations for specific pulmonary diseases and better quality control. This review describes the hydrophobic peptide analogues developed thus far and their potential for use in a new generation of synthetic surfactant preparations.

Conformational mapping of the N-terminal segment of surfactant protein B in lipid using 13C-enhanced Fourier transform infrared spectroscopy

Synthetic peptides based on the N-terminal domain of human surfactant protein B (SP-B1-25; 25 amino acid residues; NH2-FPIPLPYCWLCRALIKRIQAMIPKG) retain important lung activities of the full-length, 79-residue protein. Here, we used physical techniques to examine the secondary conformation of SP-B1-25 in aqueous, lipid and structure-promoting environments. Circular dichroism and conventional, 12C-Fourier transform infrared (FTIR) spectroscopy each indicated a predominate alpha-helical conformation for SP-B1-25 in phosphate-buffered saline, liposomes of 1-palmitoyl-2-oleoyl phosphatidylglycerol and the structure-promoting solvent hexafluoroisopropanol; FTIR spectra also showed significant beta- and random conformations for peptide in these three environments. In further experiments designed to map secondary structure to specific residues, isotope-enhanced FTIR spectroscopy was performed with 1-palmitoyl-2-oleoyl phosphatidylglycerol liposomes and a suite of SP-B1-25 peptides labeled with 13C-carbonyl groups at either single or multiple sites. Combining these 13C-enhanced FTIR results with energy minimizations and molecular simulations indicated the following model for SP-B1-25 in 1-palmitoyl-2-oleoyl phosphatidylglycerol: beta-sheet (residues 1-6), alpha-helix (residues 8-22) and random (residues 23-25) conformations. Analogous structural motifs are observed in the corresponding homologous N-terminal regions of several proteins that also share the 'saposin-like' (i.e. 5-helix bundle) folding pattern of full-length, human SP-B. In future studies, 13C-enhanced FTIR spectroscopy and energy minimizations may be of general use in defining backbone conformations at amino acid resolution, particularly for peptides or proteins in membrane environments.

Cutting edge: IL-4 production by mast cells does not require c-maf

The c-maf transcription factor is selectively expressed in IL-4-producing Th2 cells. It has been implicated in IL-4 gene transcription based on its ability to directly activate the IL-4 gene in nonexpressing B cells and to promote IL-4-induced Th2 differentiation. However, it has not been definitively shown that IL-4 production by other cells is dependent on the presence of c-maf. Here, we show that IL-4-producing mast cells do not express the c-maf factor. Furthermore, mutation of a defined c-maf binding site within the proximal IL-4 promoter, which profoundly affects transcription in T cells, has no effect on expression of a reporter gene driven by the IL-4 promoter in mast cells. These results demonstrate that c-maf and its target binding site are not required for IL-4 production in all cell types and delineate additional cis- and trans-acting elements that contribute to the cell-type specific transcriptional regulation of IL-4.

Membrane interactions of the synthetic N-terminal peptide of HIV-1 gp41 and its structural analogs

Structural and functional studies assessed the membrane actions of the N terminus of HIV-1 glycoprotein 41000 (gp41). Earlier site-directed mutagenesis has shown that key amino acid changes in this gp41 domain inhibit viral infection and syncytia formation. Here, a synthetic peptide corresponding to the N terminus of gp41 (FP; 23 residues, 519-541), and also FP analogs (FP520V/E with Val-->Glu at residue 520; FP527L/R with Leu-->Arg at 527; FP529F/Y with Phe-->Tyr at 529; and FPCLP1 with FP truncated at 525) incorporating these modifications were prepared. When added to human erythrocytes at physiologic pH, the lytic and aggregating activities of the FP analogs were much reduced over those with the wild-type FP. With resealed human erythrocyte ghosts, the lipid-mixing activities of the FP analogs were also substantially depressed over that with the wild-type FP. Combined with results from earlier studies, theoretical calculations using hydrophobic moment plot analysis and physical experiments using circular dichroism and Fourier transform infrared spectroscopy indicate that the diminished lysis and fusion noted for FP analogs may be due to altered peptide-membrane lipid interactions. These data confirm that the N-terminal gp41 domain plays critical roles in the cytolysis and fusion underlying HIV-cell infection.

Novel polyisobutylene/polydimethylsiloxane bicomponent networks: III. Tissue compatibility

The tissue biocompatibility of a series of novel rubbery polyisobutylene (PIB)/polydimethylsiloxane (PDMS) bicomponent networks was investigated by in vivo implantation into rats. Bicomponent networks of varying composition (PIB wt%/PDMS wt% = 70/30, 50/50, 35/65) as well as a standard polyethylene control were implanted intraperitoneally. After eight weeks the implants and surrounding tissue were removed for histological evaluation. In all scoring categories (i.e. collagen thickness, fibrous tissue orientation, collagen deposition in muscle tissue, lymphocyte infiltration, angiogenesis) the PIB/PDMS bicomponent network implants elicited either less or similar tissue and cellular response than polyethylene. To determine which implant elicited the least tissue and cellular response overall, a weighted score including collagen thickness, lymphocyte infiltration, and angiogenesis was calculated for each implant. According to these preliminary investigations, PIB/PDMS bicomponent networks are suitable for implant applications.

STAT6-independent production of IL-4 by mast cells

The acquisition of an IL-4-producing phenotype in Th2 cells requires IL-4 signaling through the STAT6 pathway during T cell differentiation. In this study we demonstrate that, unlike in naive T cells, IL-4 is not necessary for the development of an IL-4-producing phenotype in mast cells. Bone marrow-derived mast cell precursors from STAT6-/- mice can differentiate into mature cells that express IL-4 levels comparable to those of wild-type mast cells. In differentiated mast cells, activation in the presence of neutralizing anti-IL-4 antibodies or mutation of the consensus STAT6 sites does not diminish IL-4 promoter activity, indicating that IL-4 is not required for active transcription. Taken together, these data suggest that mast cell IL-4 production is not STAT6 dependent, providing evidence that these cells could generate IL-4 needed for the initiation and amplification of an effective Th2 immune response.

IL-4 preferentially activates a novel STAT6 isoform in mast cells

IL-4 is a pleiotropic cytokine that signals through STAT6 to direct the transactivation of multiple gene targets. In this study, we demonstrate that mast cells express a distinct STAT6 isoform. This "mast cell STAT" is a product of the STAT6 gene, but is only 65 kDa in size and appears to lack the defined C-terminal transactivation domain. Despite the presence of the conventional 94-kDa STAT6 molecule, it is the smaller isoform that associates with a consensus STAT6 binding site in extracts from IL-4-treated mast cells. This is the first evidence that STAT6 isoforms can be preferentially activated and bind to DNA in a cell-specific manner. These results imply that an additional level of specificity in the IL-4R signaling mechanism exists and may partially explain the diverse effects that IL-4 exerts on different cell types.

NF-ATc isoforms are differentially expressed and regulated in murine T and mast cells

NF of activated T cells (NF-AT) denotes a family of transcription factors that regulate the activation-dependent expression of many immunologically important proteins. At least four distinct genes encode the various family members, and several isoforms of these have been identified as well. The overlapping expression patterns and similar in vitro binding and trans-activation activities on various promoter elements of NF-AT-regulated genes suggest some redundancy in the function of these proteins. However, the phenotypic analysis of NF-AT-deficient mice supports the idea that there are tissue- and gene-specific functions as well. In this study we have characterized the expression of NF-AT cDNAs in murine mast cells. The majority of clones identified correspond to two NF-ATc isoforms that differ only in their amino-terminal sequence. Despite minimal discrepancies in the coding region, there are striking tissue- and cell type-specific differences in isoform expression patterns. Detection of NF-ATc.alpha mRNA is strictly dependent on cell activation signals in both T and mast cell lines. In contrast, the beta isoform is expressed at very low constitutive levels in both cell types but is only up-regulated in response to mast cell activation signals delivered through the FcepsilonRI or via calcium ionophores. These results demonstrate another level of regulation within the NF-AT family that can contribute to cell type-specific gene expression.

MgATP binding to the nucleotide-binding domains of the eukaryotic cytoplasmic chaperonin induces conformational changes in the putative substrate-binding domains

The eukaryotic cytosolic chaperonins are large heterooligomeric complexes with a cylindrical shape, resembling that of the homooligomeric bacterial counterpart, GroEL. In analogy to GroEL, changes in shape of the cytosolic chaperonin have been detected in the presence of MgATP using electron microscopy but, in contrast to the nucleotide-induced conformational changes in GroEL, no details are available about the specific nature of these changes. The present study identifies the structural regions of the cytosolic chaperonin that undergo conformational changes when MgATP binds to the nucleotide binding domains. It is shown that limited proteolysis with trypsin in the absence of MgATP cleaves each of the eight subunits approximately in half, generating two fragments of approximately 30 kDa. Using mass spectrometry (MS) and N-terminal sequence analysis, the cleavage is found to occur in a narrow span of the amino acid sequence, corresponding to the peptide binding regions of GroEL and to the helical protrusion, recently identified in the structure of the substrate binding domain of the archeal group II chaperonin. This proteolytic cleavage is prevented by MgATP but not by ATP in the absence of magnesium, ATP analogs (MgATPyS and MgAMP-PNP) or MgADP. These results suggest that, in analogy to GroEL, binding of MgATP to the nucleotide binding domains of the cytosolic chaperonin induces long range conformational changes in the polypeptide binding domains. It is postulated that despite their different subunit composition and substrate specificity, group I and group II chaperonins may share similar, functionally-important, conformational changes. Additional conformational changes are likely to involve a flexible helix-loop-helix motif, which is characteristic for all group II chaperonins.

Effect of carbohydrate position on lysosomal transport of procathepsin L

To study the role of carbohydrate in lysosomal protein transport, we engineered two novel glycosylation signals (Asn-X-Ser/Thr) into the cDNA of human procathepsin L, a lysosomal acid protease. We constructed six mutant cDNAs encoding glycosylation signals at mutant sites Asn-138, Asn-175, or both sites together, in the presence or absence of the wild-type Asn-204 site. We stably transfected wild-type and mutant cDNAs into NIH3T3 mouse fibroblasts and then used species-specific antibodies to determine the glycosylation status, phosphorylation, localization, and transport kinetics of recombinant human procathepsin L containing one, two, or three glycosylation sites. Both novel glycosylation sites were capable of being glycosylated, although Asn-175 was utilized only 30-50% of the time. Like the wild-type glycosylation at Asn-204, carbohydrates at Asn-138 and Asn-175 were completely sensitive to endoglycosidase H, and they were phosphorylated. Mutant proteins containing two carbohydrates were capable of being delivered to lysosomes, but there was not a consistent relationship between the efficiency of lysosomal delivery and carbohydrate content of the protein. Pulse-chase labeling revealed a unique biosynthetic pattern for proteins carrying the Asn-175 glycosylation sequence. Whereas wild-type procathepsin L and mutants bearing carbohydrate at Asn-138 appeared in lysosomes by about 60 min, proteins with carbohydrate at Asn-175 were processed to a lysosome-like polypeptide within 15 min. Temperature shift, brefeldin A, and NH4Cl experiments suggested that the rapid processing did not occur in the endoplasmic reticulum and that Asn-175 mutants could interact with the mannose 6-phosphate receptor. Taken together, our results are consistent with the interpretation that Asn-175 carbohydrate confers rapid transport to lysosomes. We may have identified a recognition domain in procathepsin L that is important for its interactions with the cellular transport machinery.

Porcine cerebroside sulfate activator (saposin B) secondary structure: CD, FTIR, and NMR studies

Cerebroside sulfate activator protein (CSAct or saposin B) is one of a group of heat stable, low-molecular-weight proteins that appear to share a common structural motif. These have been referred to as saposin-like proteins and are thought to share a multiple amphipathic helical barrel structure with a conserved pattern of disulfide linkages. Porcine kidney CSAct was prepared in high purity and consisted of three major glycosylated subforms. The protein was studied by physical-chemical methods and evaluated by various methods for structural prediction. All suggest that CSAct has high amounts of alpha-helical conformation and little if any beta-sheet. Circular dichroism (CD) studies indicate 45-50% helical conformation depending on buffer and temperature. There was only a moderate loss in helical content with increasing temperature and no indication of thermal denaturation. Fourier transform infrared spectroscopy (FTIR) measurements on deuterium hydrated self-films also indicated a predominantly helical structure. Helical axis orientation was investigated by both oriented CD and FTIR dichroism, which suggested that the helical axes were roughly parallel and oriented along the axis of the surface on which the self-films had been deposited. One-dimensional nuclear magnetic resonance spectra showed large chemical shift dispersion, indicating a defined tertiary structure with little variation between 6 and 85 degrees C. NOESY spectra failed to show the strong NOE cross peaks expected for a highly helical conformation. This may indicate short-term conformational flexibility within the helices or molecular aggregation at the high protein concentrations employed. These observations are consistent with the 3-4-helix bundle motif suggested for saposin-like proteins by various predictive algorithms.

Inefficient peptide binding by cell-surface class II MHC molecules

The efficiency of peptide loading onto surface class II MHC molecules in intact APC was investigated, using a previously defined europium immunoassay as well as a simplified Western blot procedure. Conditions normally employed for peptide loading in T cell stimulation assays were suboptimal for peptide binding, which is enhanced at low pH, in the presence of protease inhibitors, and the absence of competing serum proteins. In contrast to some earlier reports, our results indicate that the rate of peptide loading by class II molecules is not enhanced in the environment of the plasma membrane. Peptide association rates were similar for purified and cell-surface class II molecules. As previously reported, rapid peptide binding can be achieved by reconstituting class II molecules into total cellular membranes. We report that this activity is due solely to HLA-DM (which is not present at the cell surface), since it can be specifically removed by immunodepletion with an anti-DM mAb. Thus, we find no evidence for additional cellular cofactors capable of catalyzing peptide binding to class II molecules.

Design and characterization of a multisite fluorescence energy-transfer system for protein folding studies: a steady-state and time-resolved study of yeast phosphoglycerate kinase

A multisite distance-based fluorescence resonance energy-transfer assay system was developed for the study of protein folding reactions. Single- and double-cysteine substitution mutagenesis was utilized to place sulfhydryl residues throughout the tertiary structure of the bidomain enzyme yeast phosphoglycerate kinase (PGK). These reactive cysteines were covalently modified with extrinsic donor [5-[[2-(2-iodoacetamido)ethyl]amino]-1-naphthalenesulfonic acid] and acceptor (5-iodoacetamidofluorescein) fluorescent labels. A detailed experimental strategy was followed, which revealed that, when these relatively large extrinsic fluorescent labels are covalently attached to properly selected solvent-exposed residues, they do not affect the intrinsic stability of the protein. The PGK crystal structure was combined with molecular dynamics simulations of the dyes built into the protein and time-resolved anisotropy experiments, in order to estimate a more realistic orientation factor, <kappa2>*, for each donor/acceptor pair. Time-resolved and steady-state fluorescence energy-transfer experiments revealed that this distance assay, spanning six different donor-acceptor distances, is linear and accurate (to within 10-20%) over the range of 30-70 A. This distance assay system for PGK allows for the measurement of long-range changes in intra- and interdomain spatial organization during protein folding reactions. The approach which we have developed can be applied to any protein system in which unique one- and two-site cysteine residues can be engineered into a protein. In the following paper [Lillo, M. P., et al. (1997) Biochemistry 36, 11273-11281], these multisite energy-transfer pairs are utilized for stopped-flow unfolding studies.

An engineered amino-terminal domain of yeast phosphoglycerate kinase with native-like structure

Previous studies have suggested that the carboxy-terminal peptide (residues 401-415) and interdomain helix (residues 185-199) of yeast phosphoglycerate kinase, a two-domain enzyme, play a role in the folding and stability of the amino-terminal domain (residues 1-184). A deletion mutant has been created in which the carboxy-terminal peptide is attached to the amino-terminal domain (residues 1-184) plus interdomain helix (residues 185-199) through a flexible peptide linker, thus eliminating the carboxy-terminal domain entirely. CD, fluorescence, gel filtration, and NMR experiments indicated that, unlike versions described previously, this isolated N-domain is soluble, monomeric, compactly folded, native-like in structure, and capable of binding the substrate 3-phosphoglycerate with high affinity in a saturable manner. The midpoint of the guanidine-induced unfolding transition was the same as that of the native two-domain protein (Cm approximately 0.8 M). The free energy change associated with guanidine-induced unfolding was one-third that of the native enzyme, in agreement with previous studies that evaluated the intrinsic stability of the N-domain and the contribution of domain-domain interactions to the stability of PGK. These observations suggest that the C-terminal peptide and interdomain helix are sufficient for maintaining a native-like fold of the N-domain in the absence of the C-domain.

Structure of the R65Q mutant of yeast 3-phosphoglycerate kinase complexed with Mg-AMP-PNP and 3-phospho-D-glycerate

The structure of a ternary complex of the R65Q mutant of yeast 3-phosphoglycerate kinase (PGK) with magnesium 5'-adenylylimidodiphosphate (Mg-AMP-PNP) and 3-phospho-D-glycerate (3-PG) has been determined by X-ray crystallography to 2.4 angstrom resolution. The structure was solved by single isomorphous replacement, anamalous scattering, and solvent flattening and has been refined to an R-factor of 0.185, with rms deviations from ideal bond distance and angles of 0.009 angstrom and 1.78 degrees, respectively. PGK consists of two domains, with the 3-PG bound to a "basic patch" of residues from the N-terminal domain and the Mg-AMP-PNP interacting with residues from the C-terminal domain. The two ligands are separated by approximately 11 angstrom across the interdomain cleft. The model of the R65Q mutant of yeast PGK is very similar to the structures of PGK isolated from horse, pig, and Bacillus stearothermophilus (rms deviations between equivalent alpha-carbons in the individual domains < 1.0 angstrom) but exhibits substantial variations with a previously reported yeast structure (rms deviations between equivalent alpha-carbons in the individual domains of 2.9-3.2 angstrom). The most significant tertiary structural differences among the yeast R65Q, equine, porcine, and B. stearothermophilus PGK structures occur in the relative orientations of the two domains. However, the relationships between the observed conformations of PGK are inconsistent with a "hinge-bending" behavior that would close the interdomain cleft. It is proposed that the available structural and biochemical data on PGK may indicate that the basic patch primarily represents the site of anion activation and not the catalytically active binding site for 3-PG.

Probing intradomain and interdomain conformational changes during equilibrium unfolding of phosphoglycerate kinase: fluorescence and circular dichroism study of tryptophan mutants

Phosphoglycerate kinase is a monomeric protein composed of two globular domains of the alpha/beta type. Extensive domain-domain interactions involve three segments of the polypeptide chain that are distant from one another in the primary sequence: the N-terminus, the C-terminus, and a centrally located alpha-helix. In order to monitor spectroscopically the conformational changes that occur in the individual domains and at the interdomain interface during the unfolding process, we have constructed a series of single-tryptophan mutants. In addition to two previously described mutants, each with single tryptophans in the C-terminal domain (W308 and W333) [Szpikowska, B. K., Beechem, J. M., Sherman, M. A., & Mas, M. T. (1994) Biochemistry 33, 2217-2225], four new single-tryptophan mutants have been constructed: two with tryptophans located in the interdomain region (W194 and W399) and two with tryptophans in the N-terminal domain (W48 and W122). The equilibrium unfolding transitions induced by guanidine hydrochloride were monitored using far-UV CD, near-UV CD, steady-state, and time-resolved fluorescence. These studies reveal two unfolding transitions and suggest a sequential unfolding process for the mutants described in this paper. During the first transition (Cm approximately 0.5 M) the interdomain region and C-terminal domain unfold; the N-terminal domain remains relatively compact but lacks much of the tertiary structure that characterizes the native state. A hyperfluorescent intermediate is detected during this transition by tryptophan probes placed within the N-terminal domain. Complete unfolding of the N-terminal domain occurs during the second transition (Cm approximately 0.9 M).

Sequential domain unfolding in phosphoglycerate kinase: fluorescence intensity and anisotropy stopped-flow kinetics of several tryptophan mutants

Stopped-flow total intensity and anisotropy experiments on single tryptophan containing mutants of yeast phosphoglycerate kinase (PGK) located in either the carboxy-terminal domain (W308 and W333), amino-terminal domain (W48 and W122), or "hinge" region (W194 and W399) were performed. The results obtained for single tryptophans in individual domains suggest that the unfolding of PGK by guanidinium hydrochloride is a sequential process in which unfolding of the carboxy-terminal domain is followed by the unfolding of the amino-terminal domain. A kinetic intermediate has been detected which consists of an unfolded carboxy-terminal domain and an altered amino-terminal domain, identical in hydrodynamic properties with the native state, but hyperfluorescent. In contrast to the C-terminal tryptophans, which exhibit concurrent total intensity and anisotropy changes in the entire denaturant concentration range (0-->2 M), the N-terminal tryptophans experience a large increase in fluorescence intensity and a constant anisotropic environment at low concentrations of denaturant, corresponding to the first transition region of the equilibrium unfolding profile. Anisotropy changes for the N-terminal probes are observed above 1 M Gdn-HCl, the region corresponding to the second equilibrium unfolding transition. Stopped-flow experiments performed on PGK mutants with two tryptophans (i.e., with a single tryptophan in each domain) confirm that each domain unfolds independently, and that the individual site-specific mutations do not significantly alter the unfolding pathway. Unfolding kinetics experiments with tryptophans situated in the hinge reveal that the region sensed by W399 unfolds before the carboxy-terminal domain, whereas W194 senses unfolding of both domains.

DM enhances peptide binding to class II MHC by release of invariant chain-derived peptide

Major histocompatibility complex (MHC) class II molecules bind antigenic peptides rapidly after biosynthesis in antigen-presenting cells (APCs). By contrast, the rate of peptide binding to purified class II molecules is remarkably slow. We find that purified HLA-DR molecules bind peptides rapidly in the presence but not the absence of HLA-DM, a recently identified heterodimer required for efficient antigen processing. The same effect is seen with immunoprecipitated DM, suggesting that DM interacts directly with DR. Class II-associated invariant chain peptides (CLIP) are selectively and rapidly released from DR during incubation with DM at pH 5. We conclude that DM is a cofactor that enhances peptide binding to DR molecules through a mechanism involving peptide exchange.

Requirement for protein synthesis in antigen processing by B cells

The role de novo protein synthesis plays in Ag processing by B cells was investigated. Cycloheximide (CHX) inhibited Ag processing in normal and transformed B cells. B lymphoblastoid cells required a 2-6 hr longer CHX pretreatment period than splenic B cells to inhibit Ag processing function. Immunoprecipitation experiments demonstrated that the half-life of class II/invariant chain (Ii) complexes was similar in normal and transformed B cells. B lymphoblastoid cells differed from splenic B cells in that a significant fraction of total class II-associated p31 Ii was modified with sialic acid (Ip). The kinetics of loss of class II-associated Ip in CHX-treated cells correlated with loss of Ag processing function. In addition, the half-life of a subpopulation of class II molecules that are unstable in sodium dodecyl sulfate at room temperature was greater in transformed cells. Our results suggest that B lymphoblastoid cells, but not splenic B cells, contain a long-lived pool of class II/Ii complexes that can bind and present peptides generated in endosomal compartments for a significant time period after cessation of protein synthesis.

Equilibrium unfolding of yeast phosphoglycerate kinase and its mutants lacking one or both native tryptophans: a circular dichroism and steady-state and time-resolved fluorescence study

Yeast 3-phosphoglycerate kinase contains two tryptophans, both situated in the carboxy-terminal domain, and seven tyrosines, five in the amino-terminal domain, one in the domain-domain interface, and one in the carboxy-terminal domain. Site-specific mutagenesis has been used to construct two single-tryptophan mutants and one no-tryptophan mutant by replacing one or both native tryptophans, W308 and W333, with phenylalanines. The mutations have been shown to have a relatively small effect on the overall structure and enzymatic properties of the mutants. Both tryptophans are quenched in the folded state. The steady-state emission spectra and tryptophan quantum yields are the same in the single-tryptophan mutants and in the wild-type protein. Large changes in the tryptophan emission maxima and steady-state emission intensities are observed upon unfolding. Far-UV circular dichroism and steady-state as well as time-resolved fluorescence spectroscopy have been used to monitor the equilibrium unfolding transitions of these mutants and wild-type PGK. For each protein, the transitions followed by CD and steady-state fluorescence are nearly coincident, suggesting that the structural changes monitored by local fluorescence probes and ellipticity changes, which are sensitive to the changes in the overall structure, report a single cooperative transition, consistent with a two-state unfolding mechanism. Both tryptophans have three lifetimes, which follow a similar pattern as a function of denaturant concentration. The amplitude terms associated with the two longer lifetimes increase with unfolding while the short lifetime amplitude decreases. It thus appears that these population amplitudes represent markers for the unfolded and folded states, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Topography of a binding site for small amnestic peptides deduced from structure-activity studies: relation to amnestic effect of amyloid beta protein

Four peptides homologous to amyloid beta protein containing the Val-Phe-Phe (VFF) sequence administered intracerebroventricularly after training caused amnesia for footshock active avoidance training in mice. Results with VFF and other peptides containing VFF or portions thereof were used to generate a topographic map for a hypothetical binding surface for amnestic peptides, termed Z. Effects on retention of footshock active avoidance training were rationalized in terms of fit to Z, making possible design of potential memory-modulating peptidic and nonpeptidic substances. Three peptides that neither improved nor impaired retention blocked the amnestic effects of beta-(12-28), a peptide homologous to amyloid beta protein, opening the way to development of substances that can antagonize the neurotoxic effects of amyloid beta protein on neural structures and thus attenuate symptoms and progression of Alzheimer disease.

Membrane interactions influence the peptide binding behavior of DR1

We analyzed the binding of an influenza matrix protein-derived peptide, MAT(17-31), to cell surface and purified DR1. The pH dependence of peptide binding was dramatically influenced by the membrane environment. Cell surface binding was enhanced at low pH, with little or no binding detected at neutral pH and optimal binding at pH 4. By contrast, hydrogen ion concentration had minimal effect on peptide binding to purified DR1. Exposure to low pH in the absence of peptide did not affect the peptide binding capacity of cell-associated DR1. Purified DR1 was stable at low pH, excluding the possibility that enhanced binding was offset by a competing denaturation event at low pH. The striking effect of pH on peptide binding characteristic of cell surface DR1 was recovered after reconstitution of purified DR1 in B cell membranes by detergent dialysis. This behavior was partially recovered by reconstitution of full-length, but not truncated DR1 in vesicles containing purified lipid. Our results demonstrate that interactions involving membrane components influence the peptide-binding behavior of DR1.

GABA--the quintessential neurotransmitter: electroneutrality, fidelity, specificity, and a model for the ligand binding site of GABAA receptors

Alone of the known neurotransmitters, GABA is an electroneutral zwitterion (pI = 7.3) at physiological pH. This confers the highest probability of successfully traversing densely packed synaptic gaps without interacting electrostatically with charged entities enroute, making GABA a high fidelity neurotransmitter. Inhibitory tone in the nervous system is coordinately coupled with physiological activity by means of the GABA system, acidification increasing GABA formation and its Cl- channel-opening efficacy, while decreasing its removal by transport and metabolic degradation. The above, together with diminution upon acidification of the postsynaptic efficacy of glutamate on excitatory NMDA receptors constitutes a sensitively responsive mechanism by which protons control levels of neural activity, locally and globally. A model made of the GABA binding site of GABAA receptors based on H-bond and hydrophobic interactions makes it seem unlikely that any other substance known to occur in nerve tissue would give rise to a high noise level at GABAA receptors.

Preactive and interactive decision-making tendencies of less and more experienced preservice teachers

The purpose of this study was to describe the planning and interactive thoughts and decisions of less and more experienced preservice teachers (PTs). Twelve PTs, 6 less and 6 more experienced, planned, taught, and reviewed two lessons in lacrosse. While planning, the PTs were instructed to think aloud and verbalize their thoughts. After teaching, the PTs viewed six segments of their videotaped lessons and, following each segment, were presented with a set of questions, given orally. The verbal reports from the think aloud and stimulated recall sessions were audiotaped and transcribed. Descriptive analysis revealed that more experienced PTs made more information requests and decisions while planning than did less experienced PTs. During instruction, all subjects tended to teach from their plan when lessons were perceived to be progressing as planned. When lessons were perceived as not progressing as planned, the more experienced PTs tended to make lesson adjustments whereas the less experienced PTs tended to continue to teach without making any adjustment. These findings are discussed within the context of knowledge representation with implications for professional preparation.

Characterization of the structure and properties of the His 62-->Ala and Arg 38-->Ala mutants of yeast phosphoglycerate kinase: an investigation of the catalytic and activatory sites by site-directed mutagenesis and NMR

The role of two "basic patch" residues, Arg-38 and His-62, in the catalytic function and anion-dependent activation of yeast 3-phosphoglycerate kinase (PGK) was investigated by site-directed mutagenesis. Steady-state kinetics and NMR experiments were conducted to characterize the functional properties and structural integrity of the R38A and H62A mutants. The results of these studies, in combination with earlier mutagenesis experiments, suggest that Arg-38 is the only catalytically essential residue among the conserved histidines and arginines of the basic patch. It appears that, similar to the remaining basic patch residues, His-62 is important for anion-dependent activation but not for enzyme activity. Cumulative evidence from this study and from previous mutagenesis experiments suggests that the basic patch region is in effect an extended anion binding site that encompasses both the catalytic and the general anion-binding site. It is proposed that substitution of any one of the basic patch residues results in an increased localization of the catalytic site. Substrate and product may still bind to this site, but a simultaneous binding of activatory anions, required for activation, has been impaired. NMR experiments suggest that the conformational changes observed upon binding of 3-PG to wild-type PGK are necessary for anion- and substrate-dependent activation.

Site-directed mutations of arginine 65 at the periphery of the active site cleft of yeast 3-phosphoglycerate kinase enhance the catalytic activity and eliminate anion-dependent activation

The function of arginine 65, a conserved residue located at the periphery of the active site cleft in yeast 3-phosphoglycerate kinase (PGK), has been investigated by site-directed mutagenesis. Mutant enzymes with glutamine, serine and alanine at position 65 all have very similar kinetic properties. The maximum velocities, determined in the absence of sulfate anion, are approximately 100% higher than the Vmax of wild-type PGK. The Km values are increased 2- to 3-fold for ATP and 5- to 6-fold for 3-phosphoglycerate (3PG). These results demonstrate that arginine 65 is not essential for catalysis. In contrast to wild-type enzyme, the mutants are not activated by sulfate ions. In addition, steady-state kinetic experiments indicate that the mutants are no longer activated by high concentrations of either 3PG or ATP. The dissociation constants for anions were determined by spectral titrations of the R65Q mutant labeled with a chromophoric probe. The Kd for 3PG is increased 6-fold, as compared to wild-type PGK, whereas the Kd for ATP is essentially unchanged. The Kd for sulfate is decreased less than 2-fold. The suppression of substrate- and sulfate-dependent activation suggests that arginine 65 participates in the regulatory mechanism responsible for activation of the enzyme.