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Molecular Mechanism and Structural Basis of Gain of Function of STAT1 Caused by Pathogenic R274Q Mutation

Research paper by Ryoji Fujiki, Atsushi Hijikata, Tsuyoshi Shirai, Satoshi Okada, Masao Kobayashi, Osamu Ohara

Indexed on: 04 Mar '17Published on: 03 Mar '17Published in: Journal of Biological Chemistry



Abstract

Gain of function (GOF) mutations in the STAT1 gene are critical for the onset of chronic mucocutaneous candidiasis (CMC) disease. However, the molecular basis for the gain of STAT1 function remains largely unclear. Here, we investigated the structural features of STAT1 GOF residues to better understand the impact of these pathogenic mutations. We constructed STAT1 alanine mutants of the α3 helix residues of the coiled-coil domain (CCD), which are frequently found in CMC pathogenic mutations, and measured their transcriptional activities. Most of the identified GOF residues were located inside the CCD stem structure or at the protein surface of the anti-parallel dimer interface. Unlike those, R274 was adjacent to the DNA-binding domain (DBD). In addition, R274 was found to functionally interact with Q441 in the DBD. Since Q441 is located at the anti-parallel dimer contact site, Q441 reorientation by R274 mutation probably impedes formation of the dimer. Further, the statistical analysis of RNA-seq data with STAT1-deficient epithelial cells and primary T cells from a CMC patient revealed that the R274Q mutation affected gene expression levels of 66 and 76 non-overlapping RefSeq genes, respectively. Since their transcription levels were only slightly modulated by wild-type STAT1, we concluded that the R274Q mutation increased transcriptional activity, but did not change dramatically the repertoire of STAT1 targets. Hence, we provide a novel mechanism of STAT1 GOF triggered by a CMC pathogenic mutation.

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