3o85

Publication Abstract from PubMed

Box C/D ribonucleoproteins (RNP) guide the 2'-O-methylation of targeted nucleotides in archaeal and eukaryotic ribosomal RNAs. The archaeal L7Ae and eukaryotic 15.5kD box C/D RNP core protein homologs initiate RNP assembly by recognizing kink-turn (K-turn) motifs. The crystal structure of the 15.5kD core protein from the primitive eukaryote Giardia lamblia is described here to a resolution of 1.8A. Giardia 15.5kD exhibits the typical alpha-beta-alpha sandwich fold exhibited by both archaeal L7Ae and eukaryotic 15.5kD proteins. Characteristic of eukaryotic homologs, the Giardia 15.5kD protein binds the K-turn motif but not the variant K-loop motif. The highly conserved residues of loop 9, critical for RNA binding, also exhibit conformations similar to human 15.5kD when bound to the K-turn motif. However, comparative sequence analysis indicated a distinct evolutionary position between Archaea and Eukarya. Indeed, assessment of Giardia 15.5kD in denaturing experiments demonstrated an intermediate stability in protein structure when compared with the eukaryotic mouse 15.5kD and archaeal Methanocaldococcus jannaschii L7Ae proteins. Most notable was the ability of Giardia 15.5kD to assemble in vitro a catalytically active chimeric box C/D RNP utilizing the archaeal M. jannaschii Nop56/58 and fibrillarin core proteins. In contrast, a catalytically-competent chimeric RNP could not be assembled using the mouse 15.5kD protein. Collectively, these analyses suggest that the Giardia lamblia 15.5kD occupies a unique position in the evolution of this box C/D RNP core protein retaining structural and functional features characteristic of both archaeal L7Ae and higher eukaryotic 15.5kD homologs.

Comparative Analysis of the 15.5kD Box C/D snoRNP Core Protein in the Primitive Eukaryote Giardia lamblia Reveals Unique Structural and Functional Features.,Biswas S, Buhrman G, Gagnon KT, Mattos C, Brown BA, Maxwell ES Biochemistry. 2011 Mar 2. PMID:21366326^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.