Conformational variation revealed by the crystal structure of RNase U2A complexed with Ca Ion and 2'-adenylic acid at 1.03 Å resolution

Asparagine can be non-enzymatically deamidated and isomerized via succinimide to isoaspartate. this post-translational modification can potentially alter the physical properties or the function of the parent protein. asn32 of ribo-nuclease u2a from ustilago sphaerogena is known to rapidly deamidate and isomerize in alkaline conditions. the crystal structure of ribonuclease u2a complexed with 2'-adenylic acid and calcium ions was determined at 1.03 å resolution. in this structure,the region from asp29 to asp37 winds around a calcium ion,and the main-chain of asn32-gly33 adopts an extended conformation. rotation of the side-chain of asn32 could bring asn32c γ into close proximity to gly33n,in a conformation suitable for succinimide formation. the structure suggests that in solution the region around asn32-gly33 is likely to be in equilibrium between multiple conformers,with the deamidation of asn32 proceeding when the region adopts an extended conformation. © 2010 bentham science publishers ltd.