structural communications1284 doi:10.1107/S174430911203881X Acta Cryst. (2012). F68, 1284–1288Acta Crystallographica Section FStructural Biologyand CrystallizationCommunicationsISSN 1744-3091Solution structure of the cold-shock-like proteinfrom Rickettsia rickettsiiKyle P. Gerarden, a ‡ Andrew M.Fuchs, b ‡ Jonathan M. Koch, a ‡Melissa M. Mueller, a ‡ David R.Graupner, a Justin T. O’Rorke, aCaleb D. Frost, a Heather A.Heinen, a Emily R. Lackner, aScott J. Schoeller, a Paul G.House, a Francis C. Peterson c andChristopher T. Veldkamp a,c *a Department of Chemistry, University ofWisconsin-Whitewater, 800 West Main Street,Whitewater, WI 53190, USA,b Department ofBiological Sciences, University of Wisconsin-Whitewater, 800 West Main Street, Whitewater,WI 53190, USA, andc Department ofBiochemistry, The Medical College ofWisconsin, 8701 Watertown Plank Road,Milwaukee, WI 53226, USA‡ These authors contributed equally.Correspondence e-mail: veldkamc@uww.eduReceived 21 May 2012Accepted 10 September 2012PDB Reference: cold-shock-like protein, 2lssRocky Mountain spotted fever is caused by Rickettsia rickettsii infection.R. rickettsii can be transmitted to mammals, including humans, through the biteof an infected hard-bodied tick of the family Ixodidae. Since the R. rickettsiigenome contains only one cold-shock-like protein and given the essential natureof cold-shock proteins in other bacteria, the structure of the cold-shock-likeprotein from R. rickettsii was investigated. With the exception of a short ?-helixfound between ?-strands 3 and 4, the solution structure of the R. rickettsii cold-shock-like protein has the typical Greek-key five-stranded ?-barrel structurefound in most cold-shock domains. Additionally, the R. rickettsii cold-shock-likeprotein, with a ?G of unfolding of 18.4 kJ mol ?1 , has a similar stability whencompared with other bacterial cold-shock proteins.1. IntroductionIn 1906, Howard Ricketts discovered the bacterium that causesRocky Mountain spotted fever and this bacterium was ultimatelynamed Rickettsia rickettsii after him (Gross & Scha¨fer, 2011; Ricketts,1906a,b). R. rickettsii is an intracellular pathogen that is transmittedto mammals, including humans, through the bite of an infected tick(Gross & Scha¨fer, 2011; Dumler & Walker, 2005). Even with treat-ment, 5–10% of humans with an R. rickettsii infection will die ofRocky Mountain spotted fever (Dumler & Walker, 2005). Ticks canbecome infected either through bacterial transfer from an infectedtick to its eggs or by transfer from a tick biting an infected mammal(McDade & Newhouse, 1986; Azad & Beard, 1998; Burgdorfer &Varma, 1967). It is interesting that environmental stimuli, such as thechanges in temperature that the bacterium might experience whileresiding in a tick or when transferred to a mammalian host, causelimited change in relative mRNA transcription levels in R. rickettsii(Ellison et al., 2009). In particular, the relative mRNA transcriptionlevels of the R. rickettsii cold-shock-like protein (Rr-Csp) are notsignificantly changed at numerous temperatures (Ellison et al., 2009).It may be that, as with other cold-shock proteins, protein levels of Rr-Csp are determined based on translational control versus transcrip-tional control (Giuliodori et al., 2004, 2010; Horn et al., 2007).Traditionally, cold-shock proteins are thought to function as RNAchaperones during cold shock through melting and binding tomRNA, thereby reducing or preventing the formation of mRNAsecondary structure (Horn et al., 2007; Chaikam & Karlson, 2010).This allows continued translation during cold adaptation (Horn et al.,2007; Chaikam & Karlson, 2010). Cold-shock proteins have acold-shock domain structure, also termed an oligosaccharide/oligonucleotide (OB) binding fold, which consist of a five-strandedantiparallel ?-barrel that binds to single-stranded nucleic acids (Hornet al., 2007; Chaikam & Karlson, 2010). This domain architecture isalso found in eukaryotes, including plants and animals (Horn et al.,2007; Chaikam & Karlson, 2010). Other conserved structural featuresof cold-shock proteins include two nonspecific RNA-bindingsequence motifs, RNP1 and RNP2 (ribonucleoprotein motifs 1 and 2,respectively), which are involved in binding to single-stranded RNAor DNA (Horn et al., 2007; Chaikam & Karlson, 2010). Given thatRr-Csp is the only cold-shock-like protein in the R. rickettsii genome(Ellison et al., 2009) and given the essential nature of bacterial cold-shock proteins for bacterial survival, the solution structure of the
