Primary immunolocalization of androgen target cells in the human anterior cruciate ligament

To identify androgen target cells in the human anterior cruciate ligament, immunohistochemical localization of the androgen receptor was performed in 31 specimens of the ligament. All of the specimens were obtained at surgery. Seventeen specimens were from women, and 14 were from men: the average age of the patients was 45.2 years (range: 18-78 years). An immunoperoxidase method using monoclonal antibodies to the androgen receptor was employed to identify androgen target cells in the ligament. Consistent staining of the androgen receptor was demonstrable in six specimens obtained from young men 18-24 years old, and equivocal positive staining was seen in two other specimens from young men. No receptors were demonstrated by this method in any of the specimens from women or older men. Androgen receptors were localized to synoviocytes in the synovium and under the synovial lining, fibroblasts in the ligament stroma, and cells lining the blood-vessel walls of the anterior cruciate ligament. The demonstration of androgen receptors in the cells of the anterior cruciate ligament strongly suggests that male sex hormones may have an effect on the structure and composition of this ligament in young men.

Estrogen affects the cellular metabolism of the anterior cruciate ligament. A potential explanation for female athletic injury

Investigations from this laboratory have established the presence of estrogen receptors in the human anterior cruciate ligament. This study further investigates the effects of 17 beta-estradiol on the cellular proliferation and collagen synthesis of fibroblasts derived from the rabbit anterior cruciate ligament. Fibroblast proliferation and collagen synthesis in response to near log concentrations of 17 beta-estradiol (at 0.0029, 0.025, 0.25, 2.5, and 25 ng/ml) were assessed by measuring [3H]thymidine and [14C]hydroxyproline incorporation, respectively. Collagen synthesis was significantly reduced with increasing local estradiol concentration (P < 0.001). Declining collagen synthesis was first noted at a 17 beta-estradiol concentration of 0.025 ng/ml. Within normal physiologic levels of estrogen (0.025 to 0.25 ng/ml), collagen synthesis was reduced by more than 40% of control, and at pharmacologic levels of 2.5 and 25 ng/ml, by more than 50% of control. A significant reduction of fibroblast proliferation was also observed with increasing estradiol concentrations (P = 0.023). Clinically, alterations in anterior cruciate ligament cellular metabolism caused by estrogen fluctuations may change the composition of the ligament, rendering it more susceptible to injury.

Fibroblast growth factor and epidermal growth factor receptors in ligament healing

Although recent in vivo studies indicate that basic fibroblast growth factor hastens the healing and strength of the medical collateral ligament after injury, in vitro studies with epidermal growth factor and basic fibroblast growth factor have shown increased fibroblast proliferation with the exogenous administration of these growth factors. Using an established spontaneously healing rabbit injury model, the surgical transection of the medial collateral ligament was undertaken in 12 anesthetized male adult rabbits. Immunohistochemical localization using monoclonal antibodies to the basic fibroblast growth factor receptor and epidermal growth factor receptor were used to identify the distribution and relative concentrations of the individual receptors at 3, 7, 14, and 28 days after surgery. Realizing that the trophic effects of basic fibroblast growth factor and epidermal growth factor are determined exclusively by their individual receptors, this study confirms the hypothesis that basic fibroblast growth factor and epidermal growth factor receptor proteins are present and increase during the early stages of medial collateral ligament healing. The understanding of this rabbit ligament injury model has far reaching implications to ligament healing seen in humans. By elucidating the spatial and temporal regulation of the basic fibroblast growth factor and epidermal growth factor receptor proteins, exogenous growth factor therapy, once approved for human use, potentially can be synchronized with maximal protein receptor levels.

The in vivo effect of lipopolysaccharide on neuromuscular transmission in the mouse

The in vivo effect of lipopolysaccharide (endotoxin) on nerve-evoked muscle contractions and neuromuscular transmission was studied in the mouse phrenic nerve-diaphragm preparations. In lipopolysaccharide-treated mouse diaphragms it was observed that indirectly induced twitch tension was unchanged while tetanic tension significantly decreased. Neostigmine (50 nM) increased the amplitude of nerve evoked muscle contractions, while it caused partial fade of tetanic contractions (Wedensky inhibition) and accelerated the run-down of end-plate potentials (e.p.ps) evoked by repetitive nerve stimulation, in the diaphragm of saline-control mice, but not of lipopolysaccharide-treated mice. These effects of neostigmine could be abolished by ouabain (5 microM). Measurement of the quantal contents of e.p.ps revealed that ouabain (5 microM) significantly increased it in the diaphragm of saline-control mice to an extent similar to that in diaphragm of lipopolysaccharide-treated mice. Moreover, ouabain-sensitive Na+, K(+)-ATPase activity in the sciatic nerve of lipopolysaccharide-treated mice was markedly decreased. The alterations in neuromuscular transmission of the diaphragm during endotoxemia could be reversed by the administration of polymyxin B (a lipopolysaccharide neutralizer) and NG-nitro-L-arginine (a nitric oxide (NO) synthase inhibitor), suggesting that NO is involved in these lipopolysaccharide-induced alterations of neuromuscular transmission mediated by an impairment of ouabain-sensitive Na+, K(+)-ATPase activity in mouse motor nerves.

Distinct genotoxicity of phenylmercury acetate in human lymphocytes as compared with other mercury compounds

In the present study, the frequency of sister chromatid exchanges (SCEs) was assayed to evaluate the genotoxic effects of mercury nitrate (Hg2+), methylmercury chloride (CH3HgCl and phenylmercury acetate (PMA) on human lymphocytes. The free radical scavengers, catalase (CA) and superoxide dismutase (SOD) were tested for their antigenotoxic effects toward PMA. PMA (1-30 microM) increased SCE frequency in a concentration-dependent manner. However, CH3HgCl significantly increased SCE frequency only at a concentration of 20 microM, and all concentrations treated with Hg2+ did not induce a positive effect. On the other hand, we first reported that 30 microM Hg2+, 20 microM CH3HgCl and (3-30 microM) PMA significantly increased the frequency of endoreduplicated mitosis. PMA was about 3- or 5-fold more effective in inducing endoreduplication than CH3HgCl or Hg2+ at equivalent toxic concentrations, respectively. However, neither CA nor SOD in concentrations of 75 and 150 microg/ml showed antagonistic action on the genotoxic effects of PMA. The results suggest that the mechanism of PMA-induced genotoxicity is not mediated by superoxide anion nor H2O2. It is concluded that PMA, which was more effective in inducing the elevation of both SCEs and endoreduplication, may be especially hazardous of the three mercury compounds tested.

Inhibition of replication of hepatitis B virus by cytallene in vitro

The acyclic cytosine nucleoside analog cytallene [1-(4'-hydroxy-1',2'-butadienyl)cytosine], which has both (+)- and (-)-enantiomers, was evaluated for its anti-hepatitis B virus (HBV) activity in 2.2.15 cells and was found to have potent activity against HBV DNA synthesis. The R-(-)-enantiomer was found to be the more active of the cytallene enantiomers, with a 50% inhibition concentration against HBV synthesis (HBIC50) of 0.08 microM. Its antiviral activity could be reversed by deoxycytidine (dC) and less efficiently by cytidine. Upon removal of the R-(-)-enantiomer from culture medium, the synthesis of HBV DNA could reinitiate, which suggested that the antiviral action is reversible. The R-(-)-enantiomer was also found to be more cytotoxic than the S-(+)-enantiomer. The degree of cytotoxicity varied among the cell lines, with a 50% inhibition of cell growth at greater than 10 microM. The R-(-)-enantiomer had no effect on HBV RNA synthesis and mitochondrial DNA synthesis at a concentration of 10 times or more than the HBIC50. The two enantiomers cannot be deaminated by dC deaminase, and they can be phosphorylated by cytoplasmic dC kinase. The R-(-)-enantiomer of cytallene is the first acyclic cytosine analog with potent inhibitory activity against HBV similar to those of other L-(-)-ddC analogs.

Destruction of a cyropreserved meniscal allograft: a case for acute rejection

A cryopreserved nontissue-antigen-matched medial meniscus was transplanted arthroscopically into the knee of a 33-year-old cyclist. The patient had previously had an open medial menisectomy 19 years earlier and had significant symptoms. Ten weeks postoperatively, the patient underwent a second-look arthroscopy for a persistent effusion. Intraoperative cultures were obtained and all ultimately tested negative. The graft was found to be frayed throughout its length and significantly decreased in size. Its central portion had become detached from the peripheral repair while both the anterior and posterior bone blocks remained intact. Dense, inflammatory, hypertrophic synovium enveloped the entire joint. Histologically, the graft was found to be necrotic and acellular centrally, whereas the periphery was infiltrated with inflammatory leukocytes and giant cells. This histologic appearance is classical for an acute or subacute type rejection of allograft tissue.

Contribution of the anterolateral joint capsule to the mechanical stability of the ankle

Published reports describe the clinical efficacy of modified Brostrom anatomic repairs, surgical procedures that involve repair and fortification of the lateral capsuloligamentous complex of the ankle for patients suffering from chronic lateral instability of this joint. A cadaveric serial sectioning study of the anterior talofibular ligament, the calcaneofibular ligament, and the remainder of the anterolateral joint capsule was completed to quantitate the contribution of the superior portion of the anterolateral joint capsule, independent of the other two structures, to the overall mechanical stability of the lateral ankle. Using 20 fresh frozen specimens, talar tilt and anterior drawer stress radiographs were taken before and after sectioning these anatomic structures in an order established by one of two protocols. Sectioning of the superior anterolateral joint capsule caused 17% to 18% of the total displacement in a Grade II sprain simulation and 29% to 33% of the total displacement in a Grade III sprain simulation. This work suggests that disruption of the segment of ankle joint capsule superior to the anterior talofibular ligament creates approximately 30% of the overall laxity encountered in a Grade III inversion sprain, substantiating the principle of restoring the integrity of the entire anterolateral joint capsule when operating on a chronically unstable ankle.

Morphology and matrix composition during early tendon to bone healing

This study outlines the early morphologic phenomenon of tendon to bone healing in the rabbit model. Twelve skeletally mature, male New Zealand White rabbits received transplantation of the hallucis longus tendon into a 2-mm calcaneal bone tunnel. The morphologic characteristics of the healing tendon to bone interface were evaluated at 1, 2, 4, and 6 weeks after surgery by the use of conventional histology and immunohistochemical localization of collagen Types I, II, and III. Histologic analysis illustrated progressive maturation and reorganization of the tendon to bone interface with subsequent development of tissue collagen fiber continuity between the tendon and bone. Initially, diffuse immunolocalization of all three collagen types was observed within the scar tissue filling the space between the tendon and bone. During a 6-week period, reorganization of the scar tissue into an interface occurred, similar to an indirect insertion. Although a definitive fibrocartilage region did not form, Type II collagen was localized at the remodeling insertion site throughout the first 6 weeks of repair. In addition, Type III collagen fibers, resembling Sharpey's fibers, were noted to span this interface. The characterization of the insertion between tendon and bone is important to the understanding of healing in commonly used orthopaedic grafting procedures, such as anterior cruciate ligament reconstructions.

Diagnosis of anterolateral ankle impingement. Comparison between magnetic resonance imaging and clinical examination

We reviewed 22 patients who had arthroscopic evaluations and preoperative magnetic resonance imaging studies of their ankles because of chronic anterolateral ankle pain after sprains. The ability of surgeons to use the initial clinical examination to predict arthroscopically confirmed anterolateral ankle impingement was compared with the ability to predict this condition using preoperative magnetic resonance imaging. The patient population consisted of 15 men and 7 women who had an average age of 28 years. Five patients (23%) were intercollegiate athletes and 17 patients (77%) were recreational athletes. All patients reported previous traumas to the involved ankles, and all were seen with chronic ankle pain. Clinical examinations were used to assess ankle pain, swelling, range of motion, and stability. Anterolateral ankle impingement was confirmed in 18 patients (82%) with arthroscopic examination. Clinical examinations had a sensitivity of 94% and a specificity of 75% for predicting impingement, and magnetic resonance imaging had a sensitivity of 39% and a specificity of 50%. The results of this study suggest that preoperative magnetic resonance imaging examination is not beneficial or cost-effective in the diagnosis of anterolateral ankle impingement; furthermore, its use may cause further delay in treatment.

Cloning and sequence analysis of human and bovine corneal antigen (CO-Ag) cDNA: identification of host-parasite protein calgranulin C

PURPOSE

The primary structure of a cornea-associated antigen (CO-Ag) has been identified and has been implicated in the pathogenesis of Mooren's ulcer. The study designs were to isolate full-length clones encoding CO-Ag from a bovine and a human corneal cDNA library so that complete sequence analyses might further define the possible role of this protein in Mooren's ulcer.

METHODS

DNA fragments of bovine and human CO-Ag were generated using unique oligonucleotide primers and reverse transcription polymerase chain reaction. These fragments were used as probes to obtain cDNA clones from a bovine and a human corneal cDNA libraries. The clones with the longest cDNA inserts were selected for sequence analyses. Human cDNA fragment was digested with Stu I and Hind III and cloned into a expression vector, pPROEXHT, at the same restriction enzyme sites. The plasmid was transformed into E. coli cells. Correct cloning and the full-length sequence of human CO-Ag were determined by sequencing the insert cDNA.

RESULTS

The bovine cDNA insert sequence was 273 nucleotides in length for the entire mRNA coding region, 212 nucleotides in the 5' untranslated region, 83 nucleotides in the 3' untranslated region and a poly(A) tail. The DNA base sequence of this clone also contained a standard initiation codon, termination codon, and the polyadenylation signal. This cDNA predicts a protein which contains 91 amino acids with a molecular weight of 10,584 daltons. Plasmid expression vector, pPROEXHT-CO-Ag, was constructed that direct the synthesis of human CO-Ag in E. coli as fusion protein. Human CO-Ag fusion protein was purified to 90% pure with a yield of 17.2 mg per liter of the bacterial cell lysate. The nucleotide sequence of the CO-Ag cDNA insert was completely identical to human neutrophil calgranulin C. The deduced amino acid sequence was completely identical to a Ca(2+)-binding protein isolated on the surface of filarial nematodes.

CONCLUSIONS

The isolation and analysis of cDNA clones containing the complete coding sequence of bovine and human CO-Ag proteins is reported. The proteins identified by deduced amino acid sequences demonstrate 100% sequence homology with human and bovine calgranulin C. Immune recognition of calgranulin C to a filarial nematode may lead to a hyperactive autoimmune response to CO-Ag in the cornea leading to a Mooren's ulcer.

The effects of uranyl ions on neuromuscular transmission in the urinary bladder of the normal and streptozotocin-diabetic mouse

The depressant effects of uranyl nitrate on the nerve-evoked muscle contraction of urinary bladder isolated from normal and streptozotocin-diabetic mice were compared. The non-cholinergic component of the evoked bladder contraction (in the presence of atropine) was specifically sensitive to the suppressive effect of uranyl nitrate. In contrast, the cholinergic component remaining after treatment with alpha, beta-methylene ATP was rather insensitive to uranyl nitrate. The contractile responses induced by KCl, acetylcholine and ATP were also not affected by uranyl nitrate, indicating a presynaptic site of action. High Ca2+ and calmodulin inhibitors (trifluoperazine, diltiazem and W7) antagonized the suppressive effects of uranyl ions. These results suggest that the depressant effects of uranyl nitrate is mediated by a reduction of prejunctional non-cholinergic transmitter release through the calcium-calmodulin pathway. In contrast to the normal bladder, the urinary bladder of streptozotocin-diabetic mice revealed not only weaker neurogenic contractile responses to electrical field stimulation, but also a profound reduction in the depressant effect of uranyl nitrate. These findings suggest that the Ca2+ regulation of non-cholinergic neurotransmission in mouse urinary bladder may be impaired in the diabetic state.

Characterization of monoclonal antibodies to the 26-kDa glutathione S-transferase of Schistosoma japonicum

Six monoclonal antibodies (MAbs) were raised in mice against the 26-kDa glutathione S-transferase (GST) of the parasite Schistosoma japonicum. These MAbs were originally selected for their specific binding to the recombinant GST (r-GST) generated in E. coli by an enzyme-linked immunosorbent assay. A further study demonstrated that all these MAbs bound to plate-coated GST affinity-purified from the parasite Schistosoma japonicum. However, in Western blotting analysis only a single monoclonal antibody (MAb Y3D7) yielded positive binding. The binding of MAb Y3D7 on Western blotting was further characterized; specific binding was found on other GST fusion proteins and on the authentic 26-kDa GST but not the 28-kDa GST in the total soluble worm proteins from Schistosoma japonicum. Using protein-A-mediated immunoprecipitation, MAbs Y3D7 and Y5D5 precipitated r-GST while in parallel experiments the remaining MAbs did not generate r-GST precipitation. In an alternative co-precipitation experiment, r-GST was first bound to glutathione (GSH) Sepharose beads and subsequently tested for interaction with the MAbs. In this manner, all MAbs except MAb Y5D5 were co-precipitated with the complexes. Thus, these select MAbs readily reacted with GST although their binding characteristics were different. Because GST has been widely used in the generation of fusion proteins for various purposes and is a potential vaccine candidate in controlling schistosomiasis, these MAbs should prove valuable for their application to molecular biology and parasitology.

Isolation, cloning, and characterisation of a trp homologue from squid (Loligo forbesi) photoreceptor membranes

The invertebrate phototransduction system is a valuable model of the ubiquitous inositol lipid signalling system. Taking advantage of the ability to obtain relatively large amounts of retinal material from the cephalopod eye, partial protein sequence data were obtained for a 92-kDa component isolated from a detergent-insensitive cytoskeletal fraction of a squid retinal microvillar membrane preparation. Degenerate oligonucleotides, designed on the basis of these sequence data, were used to isolate a full-length cDNA, encoding the 92-kDa component, using both cDNA library screening and 5'-rapid amplification of cDNA ends (5'-RACE) techniques. Comparison of the amino acid sequence encoded by this cDNA with entries in the OWL composite protein sequence database reveals greatest sequence similarity with the products of the Drosophila trp and trpl genes. Greatest variation from the Drosophila Trp protein is seen in the carboxyl-terminal region, which is considerably truncated in the squid protein and which accounts for most of the substantial difference in molecular weight seen between these proteins. This variation may be significant as the carboxyl-terminal domain has been shown to be in the regulation of several ligand-gated channels. The carboxyl-terminal domain has been expressed and shown to interact with calmodulin in a calcium-dependent fashion, thereby supporting this hypothesis. The likely occurrence of other homologues in a variety of systems suggests that this is a novel and important family of regulated ion channels involved in calcium signalling.

A prospective evaluation of a new physical examination in predicting glenoid labral tears

We studied 62 patients (40 men and 22 women) with an average age of 28 years over a 28-month period who presented with shoulder pain that was refractory to 3 months of conservative management. Patients with a prior glenohumeral dislocation or a rotator cuff tear were excluded. The "crank" test was performed with the arm elevated to 160 degrees in the scapular plane of the body, loaded axially along the humerus, and with maximal internal and external rotation. Although similar tests have been described, the crank test is a new examination previously unreported. Half of the patients (31) had a positive crank test. Arthroscopy performed on all 62 patients revealed glenoid labral tears in 32 patients. Two patients who had positive crank tests did not have labral tears but had partial-thickness, articular-side rotator cuff tears. The sensitivity of the crank test was 91%, the specificity was 93%, the positive predictive value was 94%, and the negative predictive value was 90%. With these data, the crank test fulfills the criteria as a single physical examination test that is highly accurate for the preoperative diagnosis of glenoid labral tears. Accordingly, expensive imaging modalities currently used in this patient population may be employed less in the future.

MRI and morphology of the insertion of the patellar tendon after graft harvesting

We performed MRI on 16 patients who had had reconstruction of the anterior cruciate ligament (ACL) with a mid-third bone-patellar-tendon-bone autograft. Our aim was to assess the tendon and the site of its insertion at an average of seven years after the original operation. In four of these patients biopsies were taken from the donor site when they had revision of their original operation. MRI showed reconstitution of the tendon into the patellar defect with no evidence of bone formation. Six patients had a persistent defect in the patellar tendon itself. Histological examination of the biopsies of the donor site showed an indirect pattern of insertion with absence of the normal fibrocartilage zone. These morphological changes may adversely affect the biomechanical properties of the healed donor site and we suggest that another graft taken from this site may not be suitable for use in a further operation for reconstruction of the ACL.

Primary immunolocalization of estrogen and progesterone target cells in the human anterior cruciate ligament

To identify estrogen and progesterone target cells in the human anterior cruciate ligament immunohistochemical localization of both estrogen and progesterone receptors was performed in 17 specimens of human anterior cruciate ligament. All ligament specimens were obtained at surgery. Thirteen specimens were from women, and four were from men: the average age was 57 years (range, 18-78 years). Eleven specimens (from nine women and two men) came from total knee replacements for osteoarthritis of the knee: three (from two women and one man), from reconstructions of the anterior cruciate ligament: two (both from women), from medial meniscectomies; and one (from a man), from an amputation secondary to chondrosarcoma of the pelvis. An immunoperoxidase method using monoclonal antibodies to the estrogen and progesterone receptors was employed to identify estrogen and progesterone target cells in the anterior cruciate ligament. Staining of both receptors was demonstrable in 14 specimens and in the remaining three specimens less than 15% of the cells were stained. Both estrogen and progesterone receptors were localized to synoviocytes in the synovial lining, fibroblasts in the anterior cruciate ligament stroma and cells in the blood vessel walls of the ligament. This demonstration of receptors for estrogen and progesterone in the cells of anterior cruciate ligament suggests that female sex hormones may have an effect on its structure and composition.

Complications of type I coronoid fractures in competitive athletes: report of two cases and review of the literature

Coronoid fractures have been classified into three types. Elbow instability is a well-recognized complication of type III and less so in type II fractures. Type I fractures have generally been considered to heal uneventfully, with early range of motion. We present two cases of type I fractures in athletes that failed to improve with conservative management. One developed loose body formation and the other a fibrous nonunion with mechanical blockage of elbow flexion. Both patients responded to arthroscopic intervention and returned to full athletic activities. These cases illustrate potential complications with type I coronoid fractures in competitive athletes that should be recognized and treated early.

Inhibition of Epstein-Barr virus replication by a novel L-nucleoside, 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil

A novel L-nucleoside analog, 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil (L-FMAU), was found to be a potent and selective inhibitor of Epstein-Barr virus (EBV) replication. The decrease in the amount of viral production was concentration dependent with a 90% inhibitory concentration of approximately 5 muM. Upon removal of the drug from treated cells, virus production resumed in 21 days. Metabolism studies indicated that L-FMAU could be converted to its mono-,di- and triphosphate metabolites in both EBV producing and non-producing cells than in EBV non-producing cells. The mechanism of selectivity of L-FMAU against EBV producing cells. However, the amount of L-FMAU nucleotides formed was three times larger in EBV producing cells than in EBV non-producing cells. The mechanism of selectivity of L-FMAU against EBV does not appear to be due solely to the preferential phosphorylation of L-FMAU in EBV producing cells. The triphosphate of L-FMAU could not be utilized as a substrate by EBV DNA polymerase or the human DNA polymerases alpha, beta, gamma, or delta. Therefore, the incorporation of L-FMAU residues into viral DNA may not be the mechanism of antiviral activity. This compound appears to have a mechanism of action different from that of any other antiherpes virus nucleoside analogs. In addition, L-FMAU has very low cytotoxicity with 50% inhibition of cell growth occurring at a concentration of 1mM. Given the potent inhibitory activity of this compound against EBV and its inability to be incorporated into cellular DNA, L-FMAU analogs should be explored as a new class of anti-EBV agents.

Amino acid sequence of an immunogenic corneal stromal protein

PURPOSE

A unique cornea-associated antigen (CO-Ag) has been purified previously from stromal extracts. The protein is the target for autoantibodies in patients with Mooren's ulcer. In this study, the amino acid sequence of CO-Ag was analyzed and the structure-function properties of CO-Ag was determined.

METHODS

Purified CO-Ag was subjected to N-terminal sequencing by automated Edman degradation. Binding of calcium (Ca2+) to CO-Ag was measured by a direct (45)Ca2+ -binding assay.

RESULTS

The complete amino acid sequence of CO-Ag has been determined. The protein contains 70 amino acids in a single chain and lacks cysteine, tryptophan, and methionine residues. A computerized data base search of protein and nucleic acid sequences revealed strong homology to the Ca2+ -binding proteins of the S-100 family. The sequence of CO-Ag shows a high homology with calgranulin C (CaG-C) previously purified from pig granulocytes. The functional Ca2+ -binding sites of CO-Ag and CaG-C were different based on homology with known Ca2+ -binding domains and their Ca2+ -binding properties. There are three amino acid substitutions in the N-terminal Ca2+ -binding domain. Differences were functionally conserved and compatible, with minimum single-base changes in the codon structures. The greatest difference was located in the C-terminal Ca2+ -binding domain. Five consecutive amino acid changes from D63-K-K-G-A67 in CO-Ag to M63-Q-D-E-Q67 occurred in CaG-C. These differences alter the structure of CO-Ag, which no longer can bind Ca2+ ions. The existence of this nonfunctional Ca2+ -binding site was corroborated by its Ca2+ -binding properties. The number of Ca2+ -binding sites for the CO-Ag sub-unit is approximately half that of the CaG-C monomer, although these two proteins have a similar low binding constant of approximately 2 x 10(-4) M.

CONCLUSIONS

These results suggest that CO-Ag is a new member of the Ca2+ -binding protein of the S-100 family heretofore undescribed in the cornea. Sequence data provide an important framework to search for sequence similarity with microbial proteins as possible substrates for molecular mimicry and for the identification of possible pathogenic epitopes in CO-Ag.