Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
Structural Insights into Ribonucleoprotein Enzymes
Small nucleolar ribonucleoprotein particles (snoRNPs) comprise a unique class of enzymes that modify and process functional RNAs. The RNP enzymes contain a conserved core of protein subunits and a RNA subunit of varying sequences. The RNA subunit directs binding of the RNP enzyme to substrate RNA through simultaneous interactions with both the substrate and core proteins. The protein components are believed to catalyze the actual modification or cleavage reaction. The processes mediated by the RNP enzymes face challenges in enzyme assembly and in topological arrangement. The large and complex substrate RNA (ribosomal or spliceosomal RNA) must be able to bind reversibly to the multi-component RNP without being trapped topologically. Box H/ACA snoRNPs comprise the most complex pseudouridine synthases and are essential for ribosome and spliceosome maturation. Vertebrate telomerase is known to harbor a box H/ACA RNP subdomain that is critical to its biogenesis and stability. Significantly, mutations in each subunit of the human box H/ACA RNP have all been linked to the rare genetic disorder dyskeratosis congenita. We have obtained a substrate-bound archaeal H/ACA RNP that reveals detailed information about the protein-only active site. Comparison of currently available subcomplex structures reveals a unique mechanism of substrate docking that involves all subunits. Mutational analysis supports structural observations and further reveals the importance of a conserved protein loop and a guide-substrate RNA pocket in binding the substrate. The observed mechanisms of protein-mediated catalysis and substrate placement may be a theme among RNA-guided enzymes.
1Institute of Molecular Biophysics