Neurospora crassa CyPBP37: a cytosolic stress protein that is able to replace yeast Thi4p function in the synthesis of vitamin B1.
Recently, we identified CyPBP37 of Neurospora crassa as a binding partner of cyclophilin41. CyPBP37 function had not yet been described, although orthologs in other organisms have been implicated in the biosynthesis of the thiazole moiety of thiamine (vitamin B1) and/or stress-related pathways. Here, CyPBP37 is characterized as an abundant cytosolic protein with a functional NAD-binding site. Saccharomyces cerevisiae mutants lacking Thi4p (the CyPBP37 ortholog) are auxotrophic for vitamin B1 (thiamine) but can grow in the presence of the thiazole moiety of thiamine, suggesting a role for Thi4p in the biosynthesis of thiazole. N.crassa CyPBP37 is able to functionally replace Thi4p in yeast thiazole synthesis. Cellular fractionation studies revealed that Thi4p is a cytosolic protein in S.cerevisiae, like its ortholog CyPBP37 in N.crassa. This implies that thiamine synthesis takes place in the cytosol of both organisms and not in the mitochondria, as suggested. The expression of CyPBP37 and Thi4p is repressed by thiamine but not by thiazole in the growth medium. In addition to its function in thiazole synthesis, CyPBP37 is a stress-inducible protein. N.crassa cyclophilin41 can chaperone the folding of CyPBP37, its own binding partner.
Faou
Pierre
P
Institut für Biochemie und Molekularbiologie der Universität Freiburg i.Br., Hermann-Herder-Str. 7, D-79104 Freiburg i.Br., Germany.
Tropschug
Maximilian
M
D000595:Amino Acid Sequence; D001665:Binding Sites; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism; D015394:Molecular Structure; D009243:NAD / Q000378:metabolism; D009492:Neurospora crassa / Q000254:growth & development / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013831:Thiamine / Q000096:biosynthesis* / Q000737:chemistry
D005656:Fungal Proteins; D018832:Molecular Chaperones; D029701:Saccharomyces cerevisiae Proteins; C089358:THI4 protein, S cerevisiae; D009243:NAD; D013831:Thiamine