Cloning of the K+-ATPase of Streptococcus faecalis. Structural and evolutionary implications of its homology to the KdpB-protein of Escherichia coli.
The K+-ATPase of Streptococcus faecalis consists of a single polypeptide component of relative Mr = 78,000 and serves as an ATP-driven pump for the accumulation of potassium by the bacterial cell. The gene encoding this ATPase was isolated by immunological screening of an S. faecalis genomic library in the Escherichia coli/pUC8 host/vector system. Two independently derived clones express the full-size ATPase polypeptide. Transcription and translation of the cloned DNA apparently proceed by means of the respective S. faecalis signals. DNA sequencing revealed a gene encoding a protein of 583 amino acids and a calculated Mr of 63,070. This protein exhibits in its primary structure regions of homology with the KdpB-subunit of the K+-ATPase of E. coli and, to a lesser extent, with eukaryotic ion-motive ATPases. The hydropathy profiles and secondary structure predictions, respectively, for the S. faecalis ATPase and the E. coli KdpB-protein show striking similarity. Even regions with low homology in the amino acid sequence exhibit structural features that have clearly been conserved in the two proteins. This points to a fundamental role of these domains in the structure and/or function of these transport ATPases.