The development of Assessment of SpondyloArthritis international Society classification criteria for axial spondyloarthritis (part II): validation and final selection

OBJECTIVE

To validate and refine two sets of candidate criteria for the classification/diagnosis of axial spondyloarthritis (SpA).

METHODS

All Assessment of SpondyloArthritis international Society (ASAS) members were invited to include consecutively new patients with chronic (> or =3 months) back pain of unknown origin that began before 45 years of age. The candidate criteria were first tested in the entire cohort of 649 patients from 25 centres, and then refined in a random selection of 40% of cases and thereafter validated in the remaining 60%.

RESULTS

Upon diagnostic work-up, axial SpA was diagnosed in 60.2% of the cohort. Of these, 70% did not fulfil modified New York criteria and, therefore, were classified as having "non-radiographic" axial SpA. Refinement of the candidate criteria resulted in new ASAS classification criteria that are defined as: the presence of sacroiliitis by radiography or by magnetic resonance imaging (MRI) plus at least one SpA feature ("imaging arm") or the presence of HLA-B27 plus at least two SpA features ("clinical arm"). The sensitivity and specificity of the entire set of the new criteria were 82.9% and 84.4%, and for the imaging arm alone 66.2% and 97.3%, respectively. The specificity of the new criteria was much better than that of the European Spondylarthropathy Study Group criteria modified for MRI (sensitivity 85.1%, specificity 65.1%) and slightly better than that of the modified Amor criteria (sensitivity 82.9, specificity 77.5%).

CONCLUSION

The new ASAS classification criteria for axial SpA can reliably classify patients for clinical studies and may help rheumatologists in clinical practice in diagnosing axial SpA in those with chronic back pain.

TRIAL REGISTRATION NUMBER

NCT00328068.

Interaction of nitric oxide synthase with the postsynaptic density protein PSD-95 and alpha1-syntrophin mediated by PDZ domains

Neuronal nitric oxide synthase (nNOS) is concentrated at synaptic junctions in brain and motor endplates in skeletal muscle. Here, we show that the N-terminus of nNOS, which contains a PDZ protein motif, interacts with similar motifs in postsynaptic density-95 protein (PSD-95) and a related novel protein, PSD-93.nNOS and PSD-95 are coexpressed in numerous neuronal populations, and a PSD-95/nNOS complex occurs in cerebellum. PDZ domain interactions also mediate binding of nNOS to skeletal muscle syntrophin, a dystrophin-associated protein. nNOS isoforms lacking a PDZ domain, identified in nNOSdelta/delta mutant mice, do not associate with PSD-95 in brain or with skeletal muscle sarcolemma. Interaction of PDZ-containing domains therefore mediates synaptic association of nNOS and may play a more general role in formation of macromolecular signaling complexes.

The Assessment of SpondyloArthritis International Society classification criteria for peripheral spondyloarthritis and for spondyloarthritis in general

OBJECTIVE

To evaluate new classification criteria for peripheral spondyloarthritis (SpA) in patients with SpA with peripheral manifestations only.

METHODS

In this Assessment of SpondyloArthritis international Society (ASAS) study, two prespecified sets of criteria were compared against the European Spondylarthropathy Study Group (ESSG) and Amor criteria in newly referred consecutive patients with undiagnosed peripheral arthritis, and/or enthesitis, and/or dactylitis that usually began before 45 years of age. The clinical diagnosis (SpA vs no SpA) made by the ASAS rheumatologist served as reference standard.

RESULTS

In all, 24 ASAS centres included 266 patients, with a final diagnosis of SpA being made in 66.2%. After adjustments a final set of criteria showed the best balance between sensitivity (77.8%) and specificity (82.9%): arthritis and/or enthesitis and/or dactylitis plus (A) one or more of the following parameters: psoriasis, inflammatory bowel disease, preceding infection, human leucocyte antigen B27, uveitis, sacroiliitis on imaging, or (B) two or more other parameters: arthritis, enthesitis, dactylitis, inflammatory back pain in the past, family history of SpA. The new criteria performed better than modified versions of the ESSG (sensitivity 62.5%, specificity 81.1%) and the Amor criteria (sensitivity 39.8%, specificity 97.8%), particularly regarding sensitivity. In the entire ASAS population of 975 patients the combined use of ASAS criteria for axial SpA and ASAS criteria for peripheral SpA also had a better balance (sensitivity 79.5%, specificity 83.3%) than the modified ESSG (sensitivity 79.1%, specificity 68.8%) and Amor criteria (sensitivity 67.5%, specificity 86.7%), respectively.

CONCLUSIONS

The new ASAS classification criteria for peripheral SpA performed well in patients presenting with peripheral arthritis, enthesitis and/or dactylitis.

Interaction of EGF receptor and grb2 in living cells visualized by fluorescence resonance energy transfer (FRET) microscopy

The interaction of activated epidermal growth factor receptor (EGFR) with the Src homology 2 (SH2) domain of the growth-factor-receptor binding protein Grb2 initiates signaling through Ras and mitogen-activated protein kinase (MAP kinase) [1,2]. Activation of EGFRs by ligand also triggers rapid endocytosis of EGF-receptor complexes. To analyze the spatiotemporal regulation of EGFR-Grb2 interactions in living cells, we have combined imaging microscopy with a modified method of measuring fluorescence resonance energy transfer (FRET) on a pixel-by-pixel basis using EGFR fused to cyan fluorescent protein (CFP) and Grb2 fused to yellow fluorescent protein (YFP). Efficient energy transfer between CFP and YFP should only occur if CFP and YFP are less than 50A apart, which requires direct interaction of the EGFR and Grb2 fused to these fluorescent moieties [3]. Stimulation by EGF resulted in the recruitment of Grb2-YFP to cellular compartments that contained EGFR-CFP and a large increase in FRET signal amplitude. In particular, FRET measurements indicated that activated EGFR-CFP interacted with Grb2-YFP in membrane ruffles and endosomes. These results demonstrate that signaling via EGFRs can occur in the endosomal compartment. The work also highlights the potential of FRET microscopy in the study of subcellular compartmentalization of protein-protein interactions in living cells.

The emergence of sense organs in the wing disc of Drosophila

We have examined the origin of a set of precisely located sense organs in the notum and wing of Drosophila, in transformant flies where lacZ is expressed in the progenitor cells of the sense organs (the sensory mother cells) and in their progeny. Here we describe the temporal pattern of appearance and divisions of the sensory mother cells that will form the eleven macrochaetes and the two trichoid sensilla of the notum, and five campaniform sensilla on the wing blade. The complete pattern of sensory mother cells develops in a strict sequence that extends over most of the third larval instar and the first 10 h after puparium formation. The delay between the onset of lacZ expression and the first differentiative division ranges from 30 h, in the case of the earliest mother cells, to 2 h for the latest mother cells. The first division shows a preferential orientation which is also specific for each sensory mother cell. Up to this stage, there is no marked difference between the three types of mechanosensory organs.

Antitumor effect of beta-elemene in non-small-cell lung cancer cells is mediated via induction of cell cycle arrest and apoptotic cell death

Beta-elemene is a novel anticancer drug, which was extracted from the ginger plant. However, the mechanism of action of beta-elemene in non-small-cell lung cancer (NSCLC) remains unknown. Here we show that beta-elemene had differential inhibitory effects on cell growth between NSCLC cell lines and lung fibroblast and bronchial epithelial cell lines. In addition, beta-elemene was found to arrest NSCLC cells at G2-M phase, the arrest being accompanied by decreases in the levels of cyclin B1 and phospho-Cdc2 (Thr-161) and increases in the levels of p27(kip1) and phospho-Cdc2 (Tyr-15). Moreover, beta-elemene reduced the expression of Cdc25C, which dephosphorylates/activates Cdc2, but enhanced the expression of the checkpoint kinase, Chk2, which phosphorylates/ inactivates Cdc25C. These findings suggest that the effect of beta-elemene on G2-M arrest in NSCLC cells is mediated partly by a Chk2-dependent mechanism. We also demonstrate that beta-elemene triggered apoptosis in NSCLC cells. Our results clearly show that beta-elemene induced caspase-3, -7 and -9 activities, decreased Bcl-2 expression, caused cytochrome c release and increased the levels of cleaved caspase-9 and poly(ADP-ribose) polymerase in NSCLC cells. These data indicate that the effect of beta-elemene on lung cancer cell death may be through a mitochondrial release of the cytochrome c-mediated apoptotic pathway.

Improved identification of intracortical lesions in multiple sclerosis with phase-sensitive inversion recovery in combination with fast double inversion recovery MR imaging

BACKGROUND AND PURPOSE

Accurate detection and classification of purely intracortical lesions in multiple sclerosis (MS) are important in understanding their role in disease progression and impact on the clinical manifestations of the disease. However, detection of these lesions with conventional MR imaging remains a challenge. Although double inversion recovery (DIR) has been shown to improve the sensitivity of the detection of cortical lesions, this sequence has low signal-to-noise ratio (SNR), poor delineation of lesion borders, and is prone to image artifacts. We demonstrate that intracortical lesions can be identified and classified with greater confidence by the combination of DIR with phase-sensitive inversion recovery (PSIR) images.

MATERIALS AND METHODS

A total of 16 subjects with MS were included in this study. DIR, PSIR, and fluid-attenuated inversion recovery (FLAIR) images were acquired and inspected by 3 experts, with identification of lesions by consensus. PSIR and DIR images were jointly used to classify lesions as purely intracortical, mixed gray-white matter, and juxtacortical. The difference in the number of lesions detected in each category was compared between combined PSIR and DIR and conventional FLAIR.

RESULTS

PSIR consistently allowed a clearer classification and delineation of lesions. Combined PSIR and DIR images showed a 337% improvement in the total number of lesions detected compared with FLAIR alone. Detection of intracortical lesions was improved by 417% compared with FLAIR. Detection of mixed gray-white matter and juxtacortical lesions was improved by 396% and 130%, respectively, compared with FLAIR.

CONCLUSION

Reliable detection and classification of intracortical lesions in MS are greatly improved by combined use of PSIR and DIR.

The initial steps of biogenesis of cyanobacterial photosystems occur in plasma membranes

During oxygenic photosynthesis in cyanobacteria and chloroplasts of plants and eukaryotic algae, conversion of light energy to biologically useful chemical energy occurs in the specialized thylakoid membranes. Light-induced charge separation at the reaction centers of photosystems I and II, two multisubunit pigment-protein complexes in the thylakoid membranes, energetically drive sequential photosynthetic electron transfer reactions in this membrane system. In general, in the prokaryotic cyanobacterial cells, the thylakoid membrane is distinctly different from the plasma membrane. We have recently developed a two-dimensional separation procedure to purify thylakoid and plasma membranes from the genetically widely studied cyanobacterium Synechocystis sp. PCC 6803. Immunoblotting analysis demonstrated that the purified plasma membrane contained a number of protein components closely associated with the reaction centers of both photosystems. Moreover, these proteins were assembled in the plasma membrane as chlorophyll-containing multiprotein complexes, as evidenced from nondenaturing green gel and low-temperature fluorescence spectroscopy data. Furthermore, electron paramagnetic resonance spectroscopic analysis showed that in the partially assembled photosystem I core complex in the plasma membrane, the P700 reaction center was capable of undergoing light-induced charge separation. Based on these data, we propose that the plasma membrane, and not the thylakoid membrane, is the site for a number of the early steps of biogenesis of the photosynthetic reaction center complexes in these cyanobacterial cells.

Observation of high-energy astrophysical neutrinos in three years of IceCube data

A search for high-energy neutrinos interacting within the IceCube detector between 2010 and 2012 provided the first evidence for a high-energy neutrino flux of extraterrestrial origin. Results from an analysis using the same methods with a third year (2012-2013) of data from the complete IceCube detector are consistent with the previously reported astrophysical flux in the 100 TeV-PeV range at the level of 10(-8)  GeV cm-2 s-1 sr-1 per flavor and reject a purely atmospheric explanation for the combined three-year data at 5.7σ. The data are consistent with expectations for equal fluxes of all three neutrino flavors and with isotropic arrival directions, suggesting either numerous or spatially extended sources. The three-year data set, with a live time of 988 days, contains a total of 37 neutrino candidate events with deposited energies ranging from 30 to 2000 TeV. The 2000-TeV event is the highest-energy neutrino interaction ever observed.

Mesenchymal stromal cells infusions improve refractory chronic graft versus host disease through an increase of CD5+ regulatory B cells producing interleukin 10

Refractory chronic graft-versus-host disease (cGVHD) is a significant complication resulting from allogeneic hematopoietic stem cell transplantation (HSCT). Mesenchymal stromal cells (MSCs) have shown promise for treating refractory cGVHD, but the favorable effects of MSCs therapy in cGVHD are complex and not fully understood. In this prospective clinical study, 20 of 23 cGVHD patients had a complete response or partial response in a 12-month follow-up study. The most marked improvements in cGVHD symptoms were observed in the skin, oral mucosa and liver. Clinical improvement was accompanied by a significantly increased number of interleukin (IL)-10-producing CD5+ B cells. Importantly, CD5+ B cells from cGVHD patients showed increased IL-10 expression after MSCs treatment, which was associated with reduced inflammatory cytokine production by T cells. Mechanistically, MSCs could promote the survival and proliferation of CD5+ regulatory B cells (Bregs), and indoleamine 2, 3-dioxygenase partially participates in the MSC-mediated effects on Breg cells. Thus, CD5+ Breg cells may have an important role in the process of MSC-induced amelioration of refractory cGVHD and may provide new clues to reveal novel mechanisms of action for MSCs.

Inheritance of resistance to bacillus thuringiensis toxin (Dipel ES) in the european corn borer

Resistance in the European corn borer, Ostrinia nubilalis (Hubner), to a commercial formulation of Bacillus thuringiensis (Bt) Berliner toxin, Dipel ES, appears to be inherited as an incompletely dominant autosomal gene. This contrasts with the inheritance of resistance to Bt in other insects, where it has usually been characterized as a recessive trait. The proposed high-dose/refuge strategy for resistance management in Bt maize depends on resistance being recessive or partially recessive. If field resistance turns out to be similar to this laboratory resistance, the usefulness of the high-dose/refuge strategy for resistance management in Bt maize may be diminished.

FKBP12 binding modulates ryanodine receptor channel gating

The ryanodine receptor (RyR1)/calcium release channel on the sarcoplasmic reticulum of skeletal muscle is comprised of four 565,000-dalton RyR1s, each of which binds one FK506 binding protein (FKBP12). RyR1 is required for excitation-contraction coupling in skeletal muscle. FKBP12, a cis-trans peptidyl-prolyl isomerase, is required for the normal gating of the RyR1 channel. In the absence of FKBP12, RyR1 channels exhibit increased gating frequency, suggesting that FKBP12 "stabilizes" the channel in the open and closed states. We now show that substitution of a Gly, Glu, or Ile for Val2461 in RyR1 prevents FKBP12 binding to RyR1, resulting in channels with increased gating frequency. In the case of the V2461I mutant RyR1, normal channel function can be restored by adding FKBP12.6, an isoform of FKBP12. These data identify Val2461 as a critical residue required for FKBP12 binding to RyR1 and demonstrate the functional role for FKBP12 in the RyR1 channel complex.

Proteomics of Synechocystis sp. strain PCC 6803. Identification of periplasmic proteins in cells grown at low and high salt concentrations

Periplasmic proteins isolated by cold osmotic shock of Synechocystis sp. PCC 6803 cells were identified using 2D PAGE, MS and genome analysis. Most of the periplasmic proteins represent 'hypothetical proteins' with unknown function. A number of proteases of different specificity, and several enzymes involved in cell wall biosynthesis were also found. In salt-adapted cells, six proteins were greatly enhanced and three proteins were newly induced. Most of the salt-enhanced proteins are involved in the alteration of cell wall structure of salt-adapted cells. The precursors of all 57 periplasmic proteins identified have a signal peptide; 47 of them contain a typical Sec-dependent signal peptide, whereas 10 contain a putative twin-arginine signal peptide.

DNA methylation of leptin and adiponectin promoters in children is reduced by the combined presence of obesity and insulin resistance

OBJECTIVE

Epigenetic alterations have been suggested to be associated with obesity and related metabolic disorders. Here we examined the correlation between obesity and insulin resistance with the methylation frequency of the leptin (LEP) and adiponectin (ADIPOQ) promoters in obese adolescents with the aim to identify epigenetic markers that might be used as tools to predict and follow up the physiological alterations associated with the development of the metabolic syndrome.

SUBJECTS

One hundred and six adolescents were recruited and classified according to body mass index and homeostasis model of assessment-insulin resistance index. The circulating concentrations of leptin, adiponectin and of several metabolic markers of obesity and insulin resistance were determined by standard methods. The methylation frequency of the LEP and ADIPOQ promoters was determined by methylation-specific PCR (MS-PCR) in DNA obtained from peripheral blood samples.

RESULTS

Obese adolescents without insulin resistance showed higher and lower circulating levels of, respectively, leptin and adiponectin along with increased plasmatic concentrations of insulin and triglycerides. They also exhibited the same methylation frequency than lean subjects of the CpG sites located at -51 and -31 nt relative to the transcription start site of the LEP gene. However, the methylation frequency of these nucleotides dropped markedly in obese adolescents with insulin resistance. We found the same inverse relationship between the combined presence of obesity and insulin resistance and the methylation frequency of the CpG site located at -283 nt relative to the start site of the ADIPOQ promoter.

CONCLUSIONS

These observations sustain the hypothesis that epigenetic modifications might underpin the development of obesity and related metabolic disorders. They also validate the use of blood leukocytes and MS-PCR as a reliable and affordable methodology for the identification of epigenetic modifications that could be used as molecular markers to predict and follow up the physiological changes associated with obesity and insulin resistance.

Can the stability of protein mutants be predicted by free energy calculations?

The use of free energy simulation techniques in the study of protein stability is critically evaluated. Results from two simulations of the thermostability mutation Asn218 to Ser218 in Subtilisin are presented. It is shown that components of the free energy change can be highly sensitive to the computational details of the simulation leading to the conclusion that free energy calculations cannot currently be used to reliably predict protein stability. The different factors that undermine the reliability are discussed.

ASAS/WHO ICF Core Sets for ankylosing spondylitis (AS): how to classify the impact of AS on functioning and health

OBJECTIVE

To report on the results of a standardised consensus process agreeing on concepts typical and/or relevant when classifying functioning and health in patients with ankylosing spondylitis (AS) based on the International Classification of Functioning and Health (ICF).

METHODS

Experts in AS from different professional and geographical backgrounds attended a consensus conference and were divided into three working groups. Rheumatologists were selected from members of the Assessment of SpondyloArthritis international Society (ASAS). Other health professionals were recommended by ASAS members. The aim was to compose three working groups with five to seven participants to allow everybody's contribution in the discussions. Experts selected ICF categories that were considered typical and/or relevant for AS during a standardised consensus process by integrating evidence from preceding studies in alternating working group and plenary discussions. A Comprehensive ICF Core Set was selected for the comprehensive classification of functioning and a Brief ICF Core Set for application in trials.

RESULTS

The conference was attended by 19 experts from 12 countries. Eighty categories were included in the Comprehensive Core Set, which included 23 Body functions, 19 Body structures, 24 Activities and participation and 14 Environmental factors. Nineteen categories were selected for the Brief Core Set, which included 6 Body functions, 4 Body structures, 7 Activities and participation and 2 Environmental factors.

CONCLUSION

The Comprehensive and Brief ICF Core Sets for AS are now available and aim to represent the external reference to define consequences of AS on functioning.

Construction of folate-conjugated pRNA of bacteriophage phi29 DNA packaging motor for delivery of chimeric siRNA to nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma is a poorly differentiated upper respiratory tract cancer that highly expresses human folate receptors (hFR). Binding of folate to hFR triggers endocytosis. The folate was conjugated into adenosine 5'-monophosphate (AMP) by 1,6-hexanediamine linkages. After reverse HPLC to reach 93% purity, the folate-AMP, which can only be used for transcription initiation but not for chain extension, was incorporated into the 5'-end of bacteriophage phi29 motor pRNA. A 16:1 ratio of folate-AMP to ATP in transcription resulted in more than 60% of the pRNA containing folate. A pRNA with a 5'-overhang is needed to enhance the accessibility of the 5' folate for specific receptor binding. Utilizing the engineered left/right interlocking loops, polyvalent dimeric pRNA nanoparticles were constructed using RNA nanotechnology to carry folate, a detection marker, and siRNA targeting at an antiapoptosis factor. The chimeric pRNAs were processed into ds-siRNA by Dicer. Incubation of nasopharyngeal epidermal carcinoma (KB) cells with the dimer resulted in its entry into cancer cells, and the subsequent silencing of the target gene. Such a protein-free RNA nanoparticle with undetectable antigenicity has a potential for repeated long-term administration for nasopharyngeal carcinoma as the effectiveness and specificity were confirmed by ex vivo delivery in the animal trial.

Serum matrix metalloproteinases and tissue inhibitors of metalloproteinases in ankylosing spondylitis: MMP-3 is a reproducibly sensitive and specific biomarker of disease activity

OBJECTIVE

To submit serum levels of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) to statistical analyses to test their exact degrees of clinical usefulness as biomarkers for detecting high disease activity in ankylosing spondylitis (AS), comparing them with erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).

METHODS

Serum levels of MMP-1, -3, -9 and TIMP-1 and -2 were measured in 42 AS patients and 20 healthy controls. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) provided the gold standard for measuring disease activity. Patients with BASDAI > or =4 were regarded as having high disease activity. The results were compared with results for a separate cohort of 41 AS patients.

RESULTS

Only MMP-3 levels were significantly higher in AS patients than in healthy controls (P<0.001). Within AS patients, MMP-3 levels were also higher in patients with high disease activity compared with those with low disease activity, and correlated significantly with BASDAI (r = 0.366, P = 0.017) and functional indices (r = 0.344, P = 0.026). The correlation with BASDAI was stable in a 1-yr follow-up (r = 0.464, P = 0.095) and reproducible with two different enzyme-linked immunosorbent assays. For detecting high disease activity, the sensitivity and specificity of MMP-3 level was 69.2 and 68.8% respectively. Most importantly, using receiver operating characteristic plots to analyse the two cohorts, MMP-3 was more accurate than ESR and CRP in detecting AS patients with high disease activity (P = 0.01 and P = 0.009, respectively).

CONCLUSION

Using several analytical approaches that have never been reported previously, we showed that MMP-3 is a more useful biomarker than ESR and CRP to detect high disease activity in AS.

A 588-gene microarray analysis of the peripheral blood mononuclear cells of spondyloarthropathy patients

OBJECTIVES

To identify genes which are more highly expressed in the peripheral blood mononuclear cells (PBMC) of patients with spondyloarthropathy (SpA), rheumatoid arthritis (RA) and psoriatic arthritis (PsA), in comparison to normal subjects.

METHODS

A 588-gene microarray was used as a screening tool to select a panel of such genes from PBMC of these subjects and of normal subjects. Results were then validated by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The following genes were more highly expressed in arthritis patients than in normal subjects: macrophage differentiation marker MNDA (myeloid nuclear differentiation antigen), MRP8 and MRP14 (migratory inhibitory factor-related proteins); signalling molecules JAK3 (janus kinase 3) and MAP kinase p38 (mitogen-activated protein kinase); receptors TNFR2/p75, C-C-chemokine receptor type 1 (CCR1), C-X-C-chemokine receptor type 4 (CXCR4) and integrin beta1; and the cytokines/chemokines interleukin (IL) 1beta and IL-8. Expression of CXCR4 was unexpectedly high among all arthritis subjects. Using RT-PCR, ELISA and immunohistology, expression of stromal cell-derived factor 1 (SDF-1) was demonstrated in arthritis joints.

CONCLUSIONS

The CXCR4/SDF-1 is a potential pro-inflammatory axis for RA, PsA and SpA.

RNA-Catalyzed CoA, NAD, and FAD synthesis from phosphopantetheine, NMN, and FMN

A novel in vitro selection method was developed to isolate RNA sequences with coenzyme-synthesizing activities. We used size-heterogeneous libraries containing randomized ribonucleotide sequences of four different lengths (30N, 60N, 100N, and 140N), all with 5'-ATP initiation. Two RNAs, CoES7 (30N) and CoES21 (60N), are able to catalyze the synthesis of three common coenzymes, CoA, NAD, and FAD, from their precursors, 4'-phosphopantetheine, NMN, and FMN, respectively. Both ribozymes require divalent manganese for activities. The results support the availability of these coenzymes in an RNA world, and point to a chemical explanation for the complex bipartite structures of many coenzymes.