Endocrinology, Vol 128, 3096-3104, Copyright © 1991 by Endocrine Society

ARTICLES

Isolation of a 48.5-kDa membrane protein from Pseudomonas maltophilia which exhibits immunologic cross-reaction to the beta-subunit of human chorionic gonadotropin

S Grover, ZA McGee and WD Odell
Department of Internal Medicine, University of Utah School of Medicine, Salt Lake City 84132.

In separate studies we have shown that Pseudomonas maltophilia (American Type Culture Collection 13637) possesses an immunoglobulin Fc- binding protein. We have found that this protein prevents the application of immunoassays using monoclonal antibodies to study possible production of a CG-like material by this bacteria. Employing an immunoglobulin saturation technique to block this protein as well as a zwitterion detergent membrane solubilization technique, we now report the isolation of a membrane protein from Pseudomonas maltophilia which shows immunological relationships to the beta-subunit and carboxyl tail of human pregnancy CG. This pseudomonas immunoreactive material produced dose-response curves in the following CG immunoassays: 1) a polyclonal rabbit anti-CG equilibrium assay, 2) carboxyl tail CG equilibrium assay, and 3) two CG equilibrium assays using monoclonal antibodies. The pseudomonas CG-like protein did not react in equilibrium assays for human TSH, human LH, or free alpha-subunit of CG. The pseudomonas CG-like protein was purified by affinity chromatography. The purified protein showed only 0.25% cross-reaction with pregnancy CG in the monoclonal antibody equilibrium assays. Furthermore, the purified protein showed no binding to rat testicular CG/LH receptors, but showed avid binding to the pseudomonas CG-binding protein previously described by Richert and Ryan. The pseudomonas protein showed no binding to Concanavalin-A, which avidly binds pregnancy CG. When assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting, this protein had a mol wt of 48,500 daltons, which is larger than the mol wt of the unglycosylated beta-subunit of pregnancy CG. We conclude that pseudomonas contain a protein that has partial homology to the beta-subunit of pregnancy CG. This material does not bind to mammalian CG receptors, but does bind to a pseudomonas CG-binding site. The latter suggests it has a function, as yet unknown, in pseudomonas.

This article has been cited by other articles:

				J. G. Edwards and W. D. Odell Partial Characterization of Chorionic Gonadotropin-Like Binding Sites from the Bacteria Xanthomonas maltophilia Experimental Biology and Medicine, September 1, 2003; 228(8): 926 - 934. [Abstract] [Full Text] [PDF]