Thermal adaptation analyzed by comparison of protein sequences from mesophilic and extremely thermophilic Methanococcus species

Thermal adaptation analyzed by comparison of protein sequences from mesophilic and extremely thermophilic Methanococcus species

Department of Microbiology, University of Illinois, B103 Chemical and Life Sciences Laboratory, 601 South Goodwin Avenue, Urbana, IL 61801

Contributed by Carl R. Woese

Abstract

The genome sequence of the extremely thermophilic archaeon Methanococcus jannaschii provides a wealth of data on proteins from a thermophile. In this paper, sequences of 115 proteins from M. jannaschii are compared with their homologs from mesophilic Methanococcus species. Although the growth temperatures of the mesophiles are about 50°C below that of M. jannaschii, their genomic G+C contents are nearly identical. The properties most correlated with the proteins of the thermophile include higher residue volume, higher residue hydrophobicity, more charged amino acids (especially Glu, Arg, and Lys), and fewer uncharged polar residues (Ser, Thr, Asn, and Gln). These are recurring themes, with all trends applying to 83–92% of the proteins for which complete sequences were available. Nearly all of the amino acid replacements most significantly correlated with the temperature change are the same relatively conservative changes observed in all proteins, but in the case of the mesophile/thermophile comparison there is a directional bias. We identify 26 specific pairs of amino acids with a statistically significant (P < 0.01) preferred direction of replacement.

Footnotes

↵ * Present address: Mayo Foundation, 200 First Street, SW, Rochester, MN 55905.
↵ † P.J.H. and J.H.B. contributed equally to this work.
↵ ‡ Present address: Department of Molecular Genetics (M/C 669), College of Medicine, University of Illinois at Chicago, 900 S. Ashland Avenue, Chicago, IL 60607.
↵ § To whom reprint requests should be addressed. e-mail: gary{at}phylo.life.uiuc.edu.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. AF078607–AF078665).