Alternative translation initiation produces a short form of a spore coat protein in Bacillus subtilis

During endospore formation in Bacillus subtilis, over two dozen polypeptides are localized to the developing spore and coordinately assembled into a thick multilayered structure called the spore coat. Assembly of the coat is initiated by the expression of morphogenetic proteins SpoIVA, CotE, and SpoVID. These morphogenetic proteins appear to guide the assembly of other proteins into the spore coat. For example, SpoVID forms a complex with the SafA protein, which is incorporated into the coat during the early stages of development. At least two forms of SafA are found in the mature spore coat: a full-length form and a shorter form (SafA-C(30)) that begins with a methionine encoded by codon 164 of safA. In this study, we present evidence that the expression of SafA-C(30) arises from translation initiation at codon 164. We found only a single transcript driving expression of SafA. A stop codon engineered just upstream of a predicted ribosome-binding site near codon M164 abolished formation of full-length SafA, but not SafA-C(30). The same effect was observed with an alanine substitution at codon 1 of SafA. Accumulation of SafA-C(30) was blocked by substitution of an alanine codon at codon 164, but not by a substitution at a nearby methionine at codon 161. We found that overproduction of SafA-C(30) interfered with the activation of late mother cell-specific transcription and caused a strong sporulation block.

Expression and characterization of recombinant human alpha-3/4-fucosyltransferase III from Spodoptera frugiperda (Sf9) and Trichoplusia ni (Tn) cells using the baculovirus expression system

The human alpha-3/4-fucosyltransferase III (Fuc-TIII) participates in the synthesis of Lewis determinants. The enzyme from human sources is scarce and heterogeneous. In this paper we describe the expression of a secreted form of Fuc-TIII (SFT3) in two insect cell lines, Spodoptera frugiperda (Sf9) and Trichoplusia ni (Tn), using the baculovirus expression system. The Sf9 cells secreted approx. 0.4 unit/l (1 mg/l) of the enzyme. The Tn cells secreted approx. 3-fold this amount. A large proportion of active protein was accumulated in the two cell lines (50 and 75% respectively for Sf9 and Tn cells, on the fourth day after infection) indicating a possible limitation not only of the folding machinery, but also a saturation of the secretory pathway. SFT3 was purified by cation-exchange chromatography followed by affinity chromatography. The enzyme from the Tn cell line had a lower global charge, possibly due to post-translational modifications, such as phosphorylation or sulphation. The two glycosylation sites from SFT3 were occupied. SFT3 secreted by Sf9 cells was completely deglycosylated by peptide-N-glycanase F, whereas 50% of SFT3 secreted by Tn cells was resistant to deglycosylation by this enzyme. The apparent kinetic parameters determined with the type I acceptor were k(cat)=0.4 s(-1) and K(m)=0.87 mM for the SFT3 secreted by Tn cells, and k(cat)=0.09 s(-1) and K(m)=0.76 mM for the SFT3 secreted by Sf9 cells, indicating that the enzymes had substrate affinities within the same order of magnitude as their mammalian counterpart. Furthermore, SFT3 secreted by either cell type showed a clear preference for type 1 carbohydrate acceptors, similarly to human Fuc-TIII.

Highly potent nociceptin analog containing the Arg-Lys triple repeat

One of the structural characteristics of a neuropeptide nociceptin is the existence of Arg-Lys (RK) residues at positions 8-9 and 12-13; both RKs have been suggested to bind to the acidic amino acid cluster in the second extracellular loop of the seven transmembrane domain receptor ORL1. With a design strategy of attempting to obtain an analog that binds more strongly to the receptor's acidic cluster, we synthesized a series of nociceptin analogs in which the RK dipeptide unit was placed at positions 6-7, 10-11, or 14-15 adjacent to the parent RKs. Among these nociceptin analogs containing the RK triple repeat, [Arg-Lys(6-7)]- and [Arg-Lys(10-11)]nociceptins exhibited weak activities (6-9 and 60-90% of nociceptin, respectively) both in the receptor binding assay and in the [(35)S]GTPgammaS binding functional assay. In contrast, [Arg-Lys(14-15)]nociceptin was found to be very potent in both assays (3-fold in binding and 17-fold in GTPgammaS functional assay). [Arg-Lys(14-15)]nociceptin was the first peptide analog found to be stronger than the parent nociceptin, and structure-activity studies have suggested that the incorporated Arg-Lys(14-15) interacts with either the receptor acidic amino acid cluster or the receptor aromatic amino acid residues.

Mutational analysis of the highly conserved arginine within the Glu/Asp-Arg-Tyr motif of the alpha(1b)-adrenergic receptor: effects on receptor isomerization and activation

We have suggested previously that both the negatively and positively charged residues of the highly conserved Glu/Asp-Arg-Tyr (E/DRY) motif play an important role in the activation process of the alpha(1b)-adreneric receptor (AR). In this study, R143 of the E/DRY sequence in the alpha(1b)-AR was mutated into several amino acids (Lys, His, Glu, Asp, Ala, Asn, and Ile). The charge-conserving mutation of R143 into lysine not only preserved the maximal agonist-induced response of the alpha(1b)-AR, but it also conferred high degree of constitutive activity to the receptor. Both basal and agonist-induced phosphorylation levels were significantly increased for the R143K mutant compared with those of the wild-type receptor. Other substitutions of R143 resulted in receptor mutants with either a small increase in constitutive activity (R143H and R143D), impairment (R143H, R143D), or complete loss of receptor-mediated response (R143E, R143A, R143N, R143I). The R413E mutant displayed a small, but significant increase in basal phosphorylation despite being severely impaired in receptor-mediated response. Interestingly, all the arginine mutants displayed increased affinity for agonist binding compared with the wild-type alpha(1b)-AR. A correlation was found between the extent of the affinity shift and the intrinsic activity of the agonists. The analysis of the receptor mutants using the allosteric ternary complex model in conjunction with the results of molecular dynamics simulations on the receptor models support the hypothesis that mutations of R143 can drive the isomerization of the alpha(1b)-AR into different states, highlighting the crucial role of this residue in the activation process of the receptor.

Catechol-binding serines of beta(2)-adrenergic receptors control the equilibrium between active and inactive receptor states

The binding free energy for the interaction between serines 204 and 207 of the fifth transmembrane helix of the beta(2)-adrenergic receptor (beta(2)-AR) and catecholic hydroxyl (OH) groups of adrenergic agonists was analyzed using double mutant cycles. Binding affinities for catecholic and noncatecholic agonists were measured in wild-type and mutant receptors, carrying alanine replacement of the two serines (S204A, S207A beta(2)-AR), a constitutive activating mutation, or both. The free energy coupling between the losses of binding energy attributable to OH deletion from the ligand and from the receptor indicates a strong interaction (nonadditivity) as expected for a direct binding between the two sets of groups. However, we also measured a significant interaction between the deletion of OH groups from the receptor and the constitutive activating mutation. This suggests that a fraction of the decrease in agonist affinity caused by serine mutagenesis may involve a shift in the conformational equilibrium of the receptor toward the inactive state. Direct measurements using a transient transfection assay confirm this prediction. The constitutive activity of the (S204A, S207A) beta(2)-AR mutant is 50 to 60% lower than that of the wild-type beta(2)-AR. We conclude that S204 and S207 do not only provide a docking site for the agonist, but also control the equilibrium of the receptor between active (R*) and inactive (R) forms.

Exploration of universal cysteines in the binding sites of three opioid receptor subtypes by disulfide-bonding affinity labeling with chemically activated thiol-containing dynorphin A analogs

A ligand containing an SNpys group, i.e. 3-nitro-2-pyridinesulfenyl linked to a mercapto (or thiol) group, can bind covalently to a free mercapto group to form a disulfide bond via the thiol-disulfide exchange reaction. This SNpys chemistry has been successfully applied to the discriminative affinity labeling of mu and delta opioid receptors with SNpys-containing enkephalins [Yasunaga, T. et al. (1996) J. Biochem. 120, 459-465]. In order to explore the mercapto groups conserved at or near the ligand binding sites of three opioid receptor subtypes, we synthesized two Cys(Npys)-containing analogs of dynorphin A, namely, [D-Ala2, Cys(Npys)8]dynorphin A-(1-9) amide (1) and [D-Ala2, Cys(Npys)12]dynorphin A-(1-13) amide (2). When rat (mu and delta) or guinea pig (kappa) brain membranes were incubated with these Cys(Npys)-containing dynorphin A analogs and then assayed for inhibition of the binding of DAGO (mu), deltorphin II (delta), and U-69593 (kappa), the number of receptors decreased sharply, depending upon the concentrations of these Cys(Npys)-containing dynorphin A analogs. It was found that dynorphin A analogs 1 and 2 effectively label mu receptors (EC50 = 27-33 nM), but also label delta receptors fairly well (160-180 nM). However, for kappa receptors they showed drastically different potencies as to affinity labeling; i.e., EC50 = 210 nM for analog 1, but 10,000 nM for analog 2. Analog 2 labeled kappa receptors about 50 times more weakly than analog 1. These results suggested that dynorphin A analog 1 labels the Cys residues conserved in mu, delta, and kappa receptors, whereas analog 2 only labels the Cys residues conserved in mu and delta receptors.

Design and synthesis of para-fluorophenylalanine amide derivatives as thrombin receptor antagonists

An antagonist specific for the thrombin receptor is expected to be a remedy for thrombosis. Structure-activity studies of thrombin receptor-tethered ligand SFLLRNP have revealed the importance of the Phe-2-phenyl group in receptor recognition and the replacement of the Phe-2 by para-fluorophenylalanine [(p-F)Phe] was found to enhance its activity [Nose, T. et al. (1993) Biochem. Biophys. Res. Commun. 193, 694-699]. In order to obtain a small sized antagonist, a series of (p-F)Phe derivatives was designed and synthesized novel structural elements essential for receptor interactions being introduced at both the N and C-termini. beta-Mercaptopropionyl (betaMp) or its derivative activated by S-3-nitro-2-pyridinesulphenyl (Npys) was introduced at the N-terminus, and phenylmethyl amines were coupled to the C-terminus. All compounds were inactive when assayed for human platelet aggregation, indicating that they are not agonists. beta-Mercaptopropionyl derivatives were also inactive as antagonists. However, Npys-containing analogs were found to inhibit the agonist activity of SFLLRNP. In particular, SNpys-betaMp-(p-F)Phe-NH-R [R = -CH(C6H5)2 and -CH2-CH-(C6H5)2] potently suppressed platelet aggregation. The results suggested that (p-F)Phe can be used as a structural core to construct an effective antagonist conformation.

The duty to recontact: attitudes of genetics service providers

The term "duty to recontact" refers to the possible ethical and/or legal obligation of genetics service providers (GSPs) to recontact former patients about advances in research that might be relevant to them. Although currently this practice is not part of standard care, some argue that such an obligation may be established in the future. Little information is available, however, on the implications of this requirement, from the point of view of GSPs. To explore the opinions of genetics professionals on this issue, we sent a self-administered questionnaire to 1,000 randomly selected U.S. and Canadian members of the American Society of Human Genetics. We received 252 completed questionnaires. The major categories of respondents were physician geneticist (41%), Ph.D. geneticist (30%), and genetic counselor (18%); 72% of the total stated that they see patients. Respondents indicated that responsibility for staying in contact should be shared between health professionals and patients. Respondents were divided about whether recontacting patients should be the standard of care: 46% answered yes, 43% answered no, and 11% did not know. Those answering yes included 44% of physician geneticists, 53% of Ph.D. geneticists, and 31% of genetic counselors; answers were statistically independent of position or country of practice but were dependent on whether the respondent sees patients (43% answered yes) or not (54% answered yes). There also was a lack of consensus about the possible benefits and burdens of recontacting patients and about various alternative methods of informing patients about research advances. Analysis of qualitative data suggested that most respondents consider recontacting patients an ethically desirable, but not feasible, goal. Points to consider in the future development of guidelines for practice are presented.

Severe prenatal growth retardation, dysmorphic features, pigmentary retinopathy, and generalized absence of subcutaneous tissues: a new entity?

We report a girl with severe prenatal and postnatal growth retardation, congenital generalized absence of subcutaneous tissue, and facial and somatic changes with some similarities to Wiedemann-Rautenstrauch syndrome (WRS). However, the patient's condition is sufficiently different from those reported previously to suggest that this patient represents a new syndrome. The abnormalities observed in this patient overlap with those of WRS, Cockayne syndrome, type A (CSA), and osteodysplastic primordial dwarfism type III (OPD III), but also include choanal atresia and pigmentary retinopathy.

Deletion 3q in two patients with blepharophimosis-ptosis-epicanthus inversus syndrome (BPES)

BACKGROUND

Blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is an autosomal dominant condition mapped to chromosome 3q23. There are several reports of chromosomal abnormalities involving this region with a resultant phenotype that includes BPES.

METHOD

We reassessed two unrelated boys ages 3 and 5 with BPES and associated nonocular abnormalities. Karyotype, which had been previously reported as normal, was repeated using high-resolution banding techniques, to look specifically at 3q23. Clinical findings were tabulated and compared with previously reported cases.

RESULTS

Both patients proved to have interstitial deletions of chromosome 3, the first involving bands q22.2q25.1 and the second q22.2q24. The first patient exhibited prenatal and postnatal growth retardation, with global developmental delay, while the second patient had normal growth and development except for speech delay. Both had dysmorphic facies with BPES, flat philtrum, a thin upper lip, and small chin. In addition, the first boy had an inguinal hernia and hypospadius; the second boy had abnormal auricles and metatarsus adductus. The eight cases of interstitial deletions of 3q2 and six rearrangements involving this region have a remarkably similar phenotype.

CONCLUSIONS

Deletion of 3q23 is a recognizable contiguous gene syndrome. Microdeletions of 3q23 should be ruled out in any sporadic case of BPES especially if there are associated nonocular abnormalities.

Interaction mode of the phe-phenyl group of thrombin receptor-tethered ligand SFLLRNP in receptor activation

Phenylalanine at position 2 of thrombin receptor-tethered ligand peptide (SFLLRNP) is crucially important for the activation of thrombin receptor. Its substitution by para-fluorophenylalanine [(p-F)Phe] enhanced several times the activity in human epithelial-like SH-EP cells [Nose et al. (1993) Biochem. Biophys. Res. Commun. 193, 694-699]. To clarify the interaction mode of Phe-2-phenyl in receptor activation, a series of analogs having chemical modifications on the benzene ring of Phe-2 were synthesized and examined for their ability to induce the aggregation of human platelets. When the fluorine atom was placed at the meta or ortho position, the resulting analogs exhibited considerably diminished activity (about 10-20% of para-derivative), indicating that the substitution is allowed only at the para position. The derivative with pentafluorophenylalanine was totally devoid of activity. These results suggested that Phe-2 requires hydrogen atom(s) on the benzene ring presumably for interaction with the receptor. No activity enhancement was observed for analogs with para-chloro-, bromo-, or iodophenylalanine, indicating the importance of the high electronegativity of fluorine to intensify the dipole of CH(s) remaining in the Phe-2-benzene ring. Inactivity of analogs having para-iodophenylalanine and homophenylalanine indicated the importance of the size of para substituents, and the placement of hydroxyl, nitro, and trifluoromethyl groups at the para position led to no activity. The interaction of Phe-2 of SFLLRNP appeared to be structurally restricted to a limited space in the receptor. The results suggested the presence of face-to-edge pi-pi interaction based upon the CH/pi interaction between the ligand Phe-2-phenyl group and the receptor aromatic group.

Skeletal dysplasias with gracile bones: three new cases, including two offspring of a mother with a dwarfing condition

We describe 3 new cases of a rare form of dwarfism (so-called "lethal skeletal dysplasia with gracile bones" or "osteocraniostenosis"), a condition characterized by thin, brittle bones and death in late gestation or early neonatal life. The first was a 37-week gestation female who died at delivery. She had facial anomalies and positional abnormalities of the hands and feet. The others were male stillborn sibs, who died in utero in the third trimester. Their mother had an undiagnosed dwarfing condition associated with body asymmetry, microcephaly, and unusual facial appearance. Both fetuses were documented by ultrasound to have short limbs and probable long bone fractures late in the second trimester. At autopsy, one fetus had no spleen and the other a hypoplastic spleen. Radiographically, all three cases had very thin diaphyses, diaphyseal fractures, and thin ribs and clavicles. In contrast to the first case who had a normally mineralized calvaria, the sibs had grossly deficient calvarial mineralization. Microscopically, endochondral ossification was qualitatively normal but quantitatively deficient in all three cases. The long bones, especially those of the sibs, lacked the well-defined outer cortex in the mid-shaft normally seen by the third trimester. This failure of organization into the cortex and medulla suggests a failure of bone remodelling. Given the variable presentation in these cases, "lethal skeletal dysplasia with gracile bones" is probably a heterogeneous disorder. The recurrence in one family suggests that the mother has somatic/germline mosaicism of a lethal gene, expressed clinically as growth failure and asymmetry.

Grebe syndrome: clinical and radiographic findings in affected individuals and heterozygous carriers

Grebe syndrome is a recessively inherited acromesomelic dysplasia. We studied, clinically and radiographically, 10 affected individuals, originating from Bahia, Brazil. The phenotype is characterized by a normal axial skeleton and severely shortened and deformed limbs, with a proximo-distal gradient of severity. The humeri and femora were relatively normal, the radii/ulnae and tibiae/fibulae were short and deformed, carpal and tarsal bones were fused, and several metacarpal and metatarsal bones were absent. The proximal and middle phalanges of the fingers and toes were invariably absent, while the distal phalanges were present. Postaxial polydactyly was found in several affected individuals. Several joints of the carpus, tarsus, hand, and foot were absent. Heterozygotes presented with a variety of skeletal manifestations including polydactyly, brachydactyly, hallux valgus, and metatarsus adductus. Grebe syndrome is caused by a missense mutation in the gene encoding cartilage-derived morphogenetic protein-1.

Monozygotic twins with 45,X/46,XY mosaicism discordant for phenotypic sex

We report on two sets of monozygotic twins (MZTs) discordant for phenotypic sex ascertained at birth when the female twin was noted to have signs of the Ullrich-Turner syndrome. Cytogenetic investigations on the female of the first pair showed 45,X/46,XY mosaicism in lymphocytes but fibroblasts grown from two skin biopsies at separate sites and from gonadal tissue showed only 45,X cells. The male showed mosaicism in both blood lymphocytes and skin fibroblasts. In the second family, both twins also showed mosaicism in lymphocytes. The female had a 45,X karyotype in fibroblasts from skin and gonadal tissue, but in contrast to the first family, the male twin had a normal male karyotype in fibroblasts from skin biopsy and from connective tissue adjacent to the vas deferens. Discordant phenotypic sex in monozygotic twins is rare. As in our cases, the nine previously reported sets of MZTs all had mosaicism for sex chromosome abnormalities. A mitotic error leading to the loss of a Y chromosome prior to, accompanying, or following the twinning process would account for the reported combinations of karyotypes.

Disruption of human limb morphogenesis by a dominant negative mutation in CDMP1

Chondrodysplasia Grebe type (CGT) is an autosomal recessive disorder characterized by severe limb shortening and dysmorphogenesis. We have identified a causative point mutation in the gene encoding the bone morphogenetic protein (BMP)-like molecule, cartilage-derived morphogenetic protein-1 (CDMP-1). The mutation substitutes a tyrosine for the first of seven highly conserved cysteine residues in the mature active domain of the protein. We demonstrate that the mutation results in a protein that is not secreted and is inactive in vitro. It produces a dominant negative effect by preventing the secretion of other, related BMP family members. We present evidence that this may occur through the formation of heterodimers. The mutation and its proposed mechanism of action provide the first human genetic indication that composite expression patterns of different BMPs dictate limb and digit morphogenesis.

Discrimination of a novel type of rat brain delta opioid receptors by enkephalin analog containing structurally constrained cyclopropylphenylalanine (inverted delta Phe)

Four different stereoisomers of cyclopropylphenylalanine (inverted delta Phe) were incorporated into [D-Ala2,Leu5]enkephalin at the position 4. These conformationally restricted enkephalin analogs were evaluated for their binding characteristics to mu and delta opioid receptors in rat brain. A striking finding is that the E-(2R,3S)-isomer binds to a novel class of delta receptors and discriminates this receptor from the ordinary delta receptor. This new type of delta receptor suspected to be a receptor which suppresses the thermal analgesia mediated through mu receptor. The Z-(2R,3R)-isomer was very potent with several times more enhanced affinity to delta receptors than to mu receptors, but could not differentiate the delta receptors. The Z-(2S,3S)-isomer was weak, and E-(2S,3R)-isomer was almost inactive.

Monozygotic twins discordant for Aicardi syndrome

Aicardi syndrome is a developmental disorder characterised by agenesis of the corpus callosum, retinal lacunae, seizures, and developmental delay. It is believed to be X linked with lethality in males. We report a set of monozygotic female twins one of whom is healthy and intellectually normal while the other has the classical Aicardi phenotype with profound retardation. Family history is negative. Both had normal karyotypes. Monozygosity was established by blood grouping, chromosomal heteromorphisms, and DNA analysis using six hypervariable probes (five autosomal and one X linked) and three X linked RFLP probes. We tested the hypothesis that preferential inactivation of a different X chromosome had occurred in each girl. Methylation sensitive RFLP analysis of DNA from EBV transformed B lymphocytes and cultured skin fibroblasts using MspI/HpaII digestion and probing with M27 beta showed a very similar pattern of X inactivation in both twins with no evidence of preferential expression of one particular X chromosome. We conclude that the abnormalities in the affected twin are probably the consequence of a postzygotic mutation in early embryonic development.

Alagille syndrome is caused by mutations in human Jagged1, which encodes a ligand for Notch1

Alagille syndrome is an autosomal dominant disorder characterized by abnormal development of liver, heart, skeleton, eye, face and, less frequently, kidney. Analyses of many patients with cytogenetic deletions or rearrangements have mapped the gene to chromosome 20p12, although deletions are found in a relatively small proportion of patients (< 7%). We have mapped the human Jagged1 gene (JAG1), encoding a ligand for the developmentally important Notch transmembrane receptor, to the Alagille syndrome critical region within 20p12. The Notch intercellular signalling pathway has been shown to mediate cell fate decisions during development in invertebrates and vertebrates. We demonstrate four distinct coding mutations in JAG1 from four Alagille syndrome families, providing evidence that it is the causal gene for Alagille syndrome. All four mutations lie within conserved regions of the gene and cause translational frameshifts, resulting in gross alterations of the protein product Patients with cytogenetically detectable deletions including JAG1 have Alagille syndrome, supporting the hypothesis that haploinsufficiency for this gene is one of the mechanisms causing the Alagille syndrome phenotype.

A mutation changes ligand selectivity and transmembrane signaling preference of the neurokinin-1 receptor

We studied the biochemical properties of a genetically engineered neurokinin-1 receptor (NK1R) in which two residues lying on the extracellular edge of the fourth transmembrane domain were replaced by equivalently located elements of the neurokinin-2 receptor (G166C, Y167F NK1R mutant). The mutation produced two effects. The first is enhancement of the apparent binding affinity for heterologous tachykinins (substance K and neurokinin B) and for N- or C-terminal modified analogues of substance P, but not for substance P itself, its full-length analogues, and several peptide and nonpeptide antagonists. Only two antagonists, as exceptions, were found to exhibit a diminished affinity for the mutant receptor. The second effect is a shift in NK1R preference for distinct G protein-mediated signaling pathways. NK1R-mediated phosphoinositide hydrolysis was enhanced both in transiently and permanently transfected cells, while stimulation of cAMP accumulation did not change in transient expression experiments and was reduced in permanently expressing cells. The effect of the mutation on ligand affinity was not related to any obvious structural commonality, nor to the selectivity for different neurokinin receptors or the agonistic/antagonistic nature of the ligand. However, all ligands responding to the mutation appear to share the ability to induce phosphoinositide signaling more efficiently than cAMP responses when binding to NK1R. We suggest that the mutation shifts the internal equilibria of different functional forms of NK1R. A theoretical analysis according to a multistate allosteric model suggests that the link between binding and biological changes can result from altered stability constants of substates in the conformational space of the receptor.

The activation process of the alpha1B-adrenergic receptor: potential role of protonation and hydrophobicity of a highly conserved aspartate

In this study, a quantitative approach was used to investigate the role of D142, which belongs to the highly conserved E/DRY sequence, in the activation process of the alpha1B-adrenergic receptor (alpha1B-AR). Experimental and computer-simulated mutagenesis were performed by substituting all possible natural amino acids at the D142 site. The resulting congeneric set of proteins together with the finding that all the receptor mutants show various levels of constitutive (agonist-independent) activity enabled us to quantitatively analyze the relationships between structural/dynamic features and the extent of constitutive activity. Our results suggest that the hydrophobic/hydrophilic character of D142, which could be regulated by protonation/deprotonation of this residue, is an important modulator of the transition between the inactive (R) and active (R*) state of the alpha1B-AR. Our study represents an example of quantitative structure-activity relationship analysis of the activation process of a G protein-coupled receptor.