SOLUTION STRUCTURE AND DNA-BINDING PROPERTIES OF A THERMOSTABLE PROTEIN FROM THE ARCHAEON SULFOLOBUS-SOLFATARICUS

The archaeon Sulfolobus solfataricus expresses large amounts of a smal l basic protein, Sso7d, which was previously identified as a DNA-bindi ng protein possibly involved in compaction of DNA. We have determined the solution structure of Sso7d. The protein consists of a triple-stra nded anti-parallel beta-sheet onto which an orthogonal double-stranded beta-sheet is packed. This topology is very similar to that found in eukaryotic Src homology-3 (SH3) domains. Sso7d binds strongly (K-d < 1 0 mu M) to double-stranded DNA and protects it from thermal denaturati on. in addition, we note that epsilon-mono-methylation of lysine side chains of Sso7d is governed by cell growth temperatures, suggesting th at methylation is related to the heat-shock response.