PMID: 8603881Apr 1, 1996Paper

Amino acid sequence of an immunogenic corneal stromal protein

Investigative Ophthalmology & Visual Science
S H Liu, J D Gottsch

Abstract

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. 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. 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 struct...Continue Reading

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