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Template:STRUCTURE 2e3c

Crystal structure of the catalytic domain of pyrrolysyl-tRNA synthetase

Overview

Pyrrolysine, a lysine derivative with a bulky pyrroline ring, is the "22nd" genetically encoded amino acid. In the present study, the carboxy-terminal catalytic fragment of Methanosarcina mazei pyrrolysyl-tRNA synthetase (PylRS) was analyzed by X-ray crystallography and site-directed mutagenesis. The catalytic fragment ligated tRNA(Pyl) with pyrrolysine nearly as efficiently as the full-length PylRS. We determined the crystal structures of the PylRS catalytic fragment in the substrate-free, ATP analogue (AMPPNP)-bound, and AMPPNP/pyrrolysine-bound forms, and compared them with the previously-reported PylRS structures. The ordering loop and the motif-2 loop undergo conformational changes from the "open" states to the "closed" states upon AMPPNP binding. On the other hand, the beta7-beta8 hairpin exhibits multiple conformational states, the open, intermediate (beta7-open/beta8-open and beta7-closed/beta8-open), and closed states, which are not induced upon substrate binding. The PylRS structures with a docked tRNA suggest that the active-site pocket can accommodate the CCA terminus of tRNA when the motif-2 loop is in the closed state and the beta7-beta8 hairpin is in the open or intermediate state. The entrance of the active-site pocket is nearly closed in the closed state of the beta7-beta8 hairpin, which may protect the pyrrolysyladenylate intermediate in the absence of tRNA(Pyl). Moreover, a structure-based mutational analysis revealed that hydrophobic residues in the amino acid-binding tunnel are important for accommodating the pyrrolysine side chain and that Asn346 is essential for anchoring the side-chain carbonyl and alpha-amino groups of pyrrolysine. In addition, a docking model of PylRS with tRNA was constructed based on the aspartyl-tRNA synthetase/tRNA structure, and was confirmed by a mutational analysis.

About this Structure

2E3C is a Single protein structure of sequence from Methanosarcina mazei. Full crystallographic information is available from OCA.

Reference

Crystallographic Studies on Multiple Conformational States of Active-site Loops in Pyrrolysyl-tRNA Synthetase., Yanagisawa T, Ishii R, Fukunaga R, Kobayashi T, Sakamoto K, Yokoyama S, J Mol Biol. 2008 Feb 29;. PMID:18387634 Page seeded by OCA on Thu Apr 24 09:24:24 2008