Partial Characterization of Chorionic Gonadotropin-Like Binding Sites from the Bacteria Xanthomonas maltophilia

Abstract

The gram-negative bacterium, Xanthomonas maltophilia, has low- and high-affinity luteinizing hormone/chorionic gonadotropin (LH/CG)-binding sites, similar to the LH/CG receptor found in mammals. Although the low-affinity site binds both LH and human CG (hCG), the high-affinity site is specific for hCG. In the current investigation, these two binding sites were independently isolated from X. maltophilia for further characterization. To isolate functional binding sites, we developed a solubilization method using the detergent zwittergent 3,14 and high glycerol concentrations that allowed for the maintenance of ligand-binding integrity. Gel filtration experiments established molecular weights of 170 and 11.5 kDa for the two binding sites, which were supported by data from photoaffinity labeling and ultracentrifugation experiments. Gel filtration data also suggested the presence of a third binding site of 5.4 kDa. The 170-kDa site had a binding affinity of Kd = 12 x 10(-6) and bound both LH and hCG. The small molecular weight site had an affinity of Kd = 9.4 x 10(-8) and was CG specific. Collectively, these data demonstrate the presence of multiple hormone binding sites in X. maltophilia that differ in molecular size, binding affinity, and ligand specificity.

Human Chorionic Gonadotropin and Related Peptides: Candidate Anti-Inflammatory Therapy in Early Stages of Sepsis

“…hCG was also detected in some bacteria and yeast from patients independent of the presence of a tumor ( 36 ). hCG-like material was detected not only in microbes that were commonly found in humans such as Staphylococcus epidermidis, S. hominis, S. haemolyticus, and Candida albicans, but also in bacteria that are less common residents of human microbiota ( 68 , 70 ).…”

“…Xanthomonas maltophilia is an uncommon but emerging nosocomial pathogen that is usually resistant to widely used antibiotics ( 71 ). LHCG-binding sites were found in X. maltophilia ( 68 ). Because these lack complete functional units, some authors have hesitated to call them receptors.…”

“…While both human LH and hCG bind to LHCG low-affinity binding sites, only hCG (not human LH) can bind to LHCG high-affinity binding sites. Other glycoproteins such as LH, FSH, and TSH do not bind to them ( 61 , 68 ). Hormone binding to high-affinity LHCG-binding sites is known to stimulate cell proliferation and changes in cell morphology ( 72 ).…”

“…These changes are stimulated by hCG, hLH and Xanthomonas CG ( 72 ). The entire gene of chorionic gonadotropin has been isolated from X. maltophilia (Xanthomonas CG), was completely sequenced and showed homology to human CG and human LHCG receptor ( 46 , 68 )(See Table 2 ). The molecular weight of fungal CG is greater than the microbial CG which is greater than mammalian CGs ( 28 , 46 , 47 ) (See Tables 2 , 3 and Figure 5 ).…”

“…Although macrophages are stimulated by foreign entities, they are not able to initiate a primary immune The entire gene of chorionic gonadotropin isolated from Xanthomonas was completely sequenced and showed 46% homology in the body of hCG b-subunit in amino acid 1761-1994 and in the 25-aa region of the carboxyl-terminal of hCG (42). The DNA sequence of the LHCG-binding site was even more similar to the human receptor, with 73% homology (68). response (87).…”