Cell-surface collagen-binding protein in the procaryote Achromobacter iophagus

Abstract

Collagen and its high-molecular-weight fragments specifically induce an extracellular collagenase (EC 3.4.24.8) in the Gram-negative Achromobacter iophagus. During the induction process the inducer is concentrated on the bacterial outer membrane. Two-dimensional electrophoresis of 125I-labelled outer membrane proteins has shown that, in particular, the amount of one protein which is already present on the surface of non-induced bacteria increases quantitatively when the inducer is added. After 125I-labelling of the cell membrane and its solubilization, the same protein is retained selectively on a gelatin-Sepharose column. It has isoelectric point of 4.9–5.1 and molecular weight of 40 000. This molecular weight is close to that of the 35 000 of the collagenase subunit. However, their non-identity was proved in three independent ways: upon two-dimensional electrophoresis, only those proteins in the range corresponding to the collagenase dimer ( M r 70 000–80 000) react with fluorescent anticollagenase antibody system, whereas the spot of the collagen-binding protein ( M r 40 000) is negative; the solubilized collagen-binding protein is not retained by anticollagenase-Sepharose affinity chromatography; in vivo, it is not protected by anti-collagenase antibodies against lactoperoxidase iodination. A hypothesis for the possible role of the collagen-binding protein in the induction of collagenase is proposed.