The 5.6-kilodalton protein in isolated chlorosomes of chloroflexus aurantiacus strain ok-70-fl is a degradation product

Abstract

Chlorosom es containing BChl a 790 have been isolated from Chloroflexus aurantiacus on sucrose density gradients using the detergents M iranol, D eriphat, N, N -dim ethyldodecylam ine-N -oxide, and dodecyl-ß-D-m altoside. All freshly prepared sam ples either lack the polypeptide of approxim ately 5 kD a, which appears identical w ith the 5.6-kD a protein previously assigned the role of BChl c-binding [R. G. Feick and R. C. Fuller, Biochem istry 23, 3693-3700 (1984)], or they contain only a minor amount there of. This polypeptide accum ulates in the chlorosom es in vitro at room tem perature w ithin 24 h after isolation. The reaction cannot be prevented simply by addition of the protease inhibitors benzamidine, £-caproic acid, and phenylm ethylsulfonyl fluoride. H owever, upon denaturation, as required to r gel electrophoresis, of the freshly isolated chlorosome sample the form ation of the 5-kD a polypeptide is inhibited. We conclude th at this species, viz. 5.6-kD a protein, is a degradation product of another - as yet unidentified - protein present in the chlorosom e preparations. Despite the pronounced proteolytic activity which affords the 5-kD a fragm ent, the native absorption and fluorescence properties of BChl c and BChl a are essentially not changed in these chlorosome preparations. © 1990, Walter de Gruyter. All rights reserved.