The crystal structure of the ttCsaA protein: an export-related chaperone from Thermus thermophilus

• Published in: The EMBO journal Vol. 20; no. 3; pp. 562 - 569
• Main Authors: Kawaguchi, Shin-ichi, Müller, Jörg, Linde, Dirk, Kuramitsu, Seiki, Shibata, Takehiko, Inoue, Yorinao, Vassylyev, Dmitry G., Yokoyama, Shigeyuki
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.02.2001; Blackwell Publishing Ltd; Oxford University Press
• Subjects: Amino Acid Sequence; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Base Sequence; chaperone; chaperones; crystal structure; Crystallography, X-Ray; CsaA protein; Dimerization; DNA Primers - genetics; Models, Molecular; Molecular Chaperones - chemistry; Molecular Chaperones - genetics; Molecular Sequence Data; protein export; Protein Structure, Quaternary; Protein Subunits; Sequence Homology, Amino Acid; Thermus thermophilus; Thermus thermophilus - chemistry; Thermus thermophilus - genetics; tRNA; ttCsaA protein
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/20.3.562

The CsaA protein was first characterized in Bacillus subtilis as a molecular chaperone with export‐related activities. Here we report the 2.0 Å‐resolution crystal structure of the Thermus thermophilus CsaA protein, designated ttCsaA. Atomic structure and experiments in solution revealed a homodimer as the functional unit. The structure of the ttCsaA monomer is reminiscent of the well known oligonucleotide‐binding fold, with the addition of extensions at the N‐ and C‐termini that form an extensive dimer interface. The two identical, large, hydrophobic cavities on the protein surface are likely to constitute the substrate binding sites. The CsaA proteins share essential sequence similarity with the tRNA‐binding protein Trbp111. Structure‐based sequence analysis suggests a close structural resemblance between these proteins, which may extend to the architecture of the binding sites at the atomic level. These results raise the intriguing possibility that CsaA proteins possess a second, tRNA‐binding activity in addition to their export‐related function.