x-ray structures of the signal recognition particle receptor reveal targeting cycle intermediatesx射线结构的信号识别颗粒受体揭示针对循环中间体.pdfVIP

X-ray Structures of the Signal Recognition Particle Receptor Reveal Targeting Cycle Intermediates 1¤ 2,3 2,3 3 Christopher L. Reyes , Earl Rutenber , Peter Walter , Robert M. Stroud * 1 Graduate Group in Biophysics, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California, United States of America, 2 Howard Hughes Medical Institute, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California, United States of America, 3 Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California, United States of America The signal recognition particle (SRP) and its conjugate receptor (SR) mediate cotranslational targeting of a subclass of proteins destined for secretion to the endoplasmic reticulum membrane in eukaryotes or to the plasma membrane in prokaryotes. Conserved active site residues in the GTPase domains of both SRP and SR mediate discrete conformational changes during formation and dissociation of the SRP ?SR complex. Here, we describe structures of the prokaryotic SR, FtsY, as an apo protein and in two different complexes with a non-hydrolysable GTP analog (GMPPNP). These structures reveal intermediate conformations of FtsY containing GMPPNP and explain how the conserved active site residues position the nucleotide into a non-catalytic conformation. The basis for the lower specificity of binding of nucleotide in FtsY prior to heterodimerization with the SRP conjugate Ffh is also shown. We propose that these structural changes represent discrete conformational states assumed by FtsY during targeting complex formation and dissociation. Citation: Reyes CL, Rutenber E, Walter P, Stroud RM (2007) X-ray Structures of the