EVOLUTION OF THE SELF-REPRODUCING SYSTEM TO THE BIOSYNTHESIS OF THE MEMBRANE - AN APPROACH FROM THE AMINO-ACID-SEQUENCE SIMILARITY IN PROTEINS

In order to study the problem of how the biomembrane synthesis started in the evolutionary process of the self-reproducing system, we carry out an extensive similarity search of the sequence data stored in data bases, using the acetyl-CoA carboxylase, fatty acid synthase and the e nzyme proteins leading to the combination of sn-glycerol 3-phosphate a nd fatty acid as the query sequences. With the use of the FASTA progra m (Pearson & Lipman, 1988), the proteins that carry an amino acid sequ ence showing similarity to any of the query sequences are picked up un der the criterion of statistical significance of more than 6.0 for the homology, then classified according to the functional blocks where th ey operate. Finally they are filtered to the enzyme proteins in the me tabolic pathways and to the DNA- or RNA-interacting proteins in the tr anslation, transcription and replication apparatuses by eliminating pr oteins such as membrane proteins, lipase etc. which seem to have been generated after the appearance of the biomembrane. The distribution of the proteins thus selected shows a clear pattern that the amino acid sequences showing considerable similarity to the biomembrane synthetic proteins are concentrically found in the enzyme proteins in and aroun d the section of glycolytic pathway from glyceraldehyde 3-phosphate to pyruvate while the DNA- or RNA-interacting proteins similar to the qu ery sequences are distributed sparsely over the translation, transcrip tion and replication systems. The assignment of similarity regions asc ertains that considerable regions of most biomembrane synthetic protei ns are covered by the enzyme proteins in and around the glycolytic pat hway. Although acetyl-CoA carboxylase and fatty acid synthase are full of variety in the constitution of active domains depending on species , the above-mentioned pattern is also obtained by using either the mon ofunctional or the multifunctional type of proteins as the query seque nces. Thus, the evolution towards biomembrane synthesis may be positio ned as an event following the establishment of a section of glycolytic pathway from glyceraldehyde 3-phosphate to pyruvate. The causality of this evolution from the glycolytic pathway to the biomembrane synthes is is also discussed in connection with the absorption of protons rele ased in the glycolytic process. (C) 1996 Academic Press Limited