Molecular and structural characterization of GTP-cyclohydrolase II in Eremothecium ashbyi NRRL Y-1363: cDNA cloning, comparative sequence analysis and molecular modeling.

GTP-cyclohydrolase II (GCH II) encoded by RIB1 gene catalyzes the first committed step in the riboflavin biosynthetic pathway. We report here the cloning and characterization of the entire RIB1 ORF (EaRIB1) of 942bp by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE-PCR) in Eremothecium ashbyi where it was found to be present as a single-copy gene. EaRIB1 sequence is available at the GenBank Accession Number EF565374. The putative peptide of 313-aa has a high similarity of 60-70% with GCH II sequences from other ascomycete fungi. Gene expression and alignment studies confirmed the functional annotation of this gene. Homology model was developed with Escherichia coli (PDB 2BZ1) as template to identify the catalytic domains and to explore its functional architecture. We report here the first three-dimensional model of any fungal GCH II which due to its absence in humans assumes significance for anti-fungal drug targeting.