Showing papers by "Raphael Guerois published in 2007"

Structural and Functional Analysis of SGT1 Reveals That Its Interaction with HSP90 Is Required for the Accumulation of Rx, an R Protein Involved in Plant Immunity

Abstract: SGT1 (for suppressor of G2 allele of skp1) and RAR1 (for required for Mla12 resistance) are highly conserved eukaryotic proteins that interact with the molecular chaperone HSP90 (for heat shock protein90). In plants, SGT1, RAR1, and HSP90 are essential for disease resistance triggered by a number of resistance (R) proteins. Here, we present structural and functional characterization of plant SGT1 proteins. Random mutagenesis of Arabidopsis thaliana SGT1b revealed that its CS (for CHORD-SGT1) and SGS (for SGT1 specific) domains are essential for disease resistance. NMR-based interaction surface mapping and mutational analyses of the CS domain showed that the CHORD II domain of RAR1 and the N-terminal domain of HSP90 interact with opposite sides of the CS domain. Functional analysis of the CS mutations indicated that the interaction between SGT1 and HSP90 is required for the accumulation of Rx, a potato (Solanum tuberosum) R protein. Biochemical reconstitution experiments suggest that RAR1 may function to enhance the SGT1–HSP90 interaction by promoting ternary complex formation.

Mechanisms of Checkpoint Kinase Rad53 Inactivation after a Double-Strand Break in Saccharomyces cerevisiae

Abstract: In Saccharomyces cerevisiae, double-strand breaks (DSBs) activate DNA checkpoint pathways that trigger several responses including a strong G2/M arrest. We have previously provided evidence that the phosphatases Ptc2 and Ptc3 of the protein phosphatase 2C type are required for DNA checkpoint inactivation after a DSB and probably dephosphorylate the checkpoint kinase Rad53. In this article we have investigated further the interactions between Ptc2 and Rad53. We showed that forkhead-associated domain 1 (FHA1) of Rad53 interacts with a specific threonine of Ptc2, T376, located outside its catalytic domain in a TXXD motif which constitutes an optimal FHA1 binding sequence in vitro. Mutating T376 abolishes Ptc2 interaction with the Rad53 FHA1 domain and results in adaptation and recovery defects following a DSB. We found that Ckb1 and Ckb2, the regulatory subunits of the protein kinase CK2, are necessary for the in vivo interaction between Ptc2 and the Rad53 FHA1 domain, that Ckb1 binds Ptc2 in vitro and that ckb1Δ and ckb2Δ mutants are defective in adaptation and recovery after a DSB. Our data thus strongly suggest that CK2 is the kinase responsible for the in vivo phosphorylation of Ptc2 T376.

HMM-Kalign

Abstract: Summary: Recent development of strategies using multiple sequence alignments (MSA) or profiles to detect remote homologies between proteins has led to a significant increase in the number of proteins whose structures can be generated by comparative modeling methods. However, prediction of the optimal alignment between these highly divergent homologous proteins remains a difficult issue. We present a tool based on a generalized Viterbi algorithm that generates optimal and sub-optimal alignments between a sequence and a Hidden Markov Model. The tool is implemented as a new function within the HMMER package called hmmkalign. Availability: http://www-spider.cea.fr/Groups/hk3039/view.html Supplementary information: Supplementary data are available at Bioinformatics online.