Isolation and molecular and functional properties of the amino‐terminal domain of colicin A

Abstract

A plasmid was constructed which allowed easy and efficient production and purification of the NH2‐terminal domain of colicin A. In only three steps, an homogenous 18‐kDa polypeptide was obtained. The NH2‐ and COOH‐terminal sequences of the protein were determined and showed that it corresponded to the NH2‐terminal 171 amino acid residues of the 63‐kDa colicin A. Although colicin A is a highly asymmetric protein, hydrodynamic studies indicated that the NH2‐terminal domain (designated AT) has a globular structure. This fragment is not the receptor‐binding domain of colicin A but is required for the transfer of colicin A across the outer membrane of sensitive cells. However, it has a low affinity for phospholipid films and this affinity is not pH‐dependent, in contrast to that of colicin A. Copyright © 1989, Wiley Blackwell. All rights reserved