D. melanogaster "Kynurenine formamidase". - Marygold, S.J. (2020)
A FlyBase (FB2020_01) search for "arylformamidase activity" (GO:0004061) returns 3 genes: Kf1?Kynurenine formamidase 1 (unannotated, FBgn0001304) - Cytogenetic Map:91B-93F (3R) Kf2?Kynurenine formamidase 2 (unannotated, FBgn0001305) - Cytogenetic Map:25A-27E (2L) KFase, Kynurenine formamidase (CG9542, FBgn0031821) - Cytogenetic Map:26D9-26D9 (2L) The unannotated (i.e. not localized to the genome) genes Kf1 and Kf2 are associated with only two papers in FlyBase: Moore, G.P., Sullivan, D.T. (1975). The characterization of multiple forms of kynurenine formidase in Drosophila melanogaster. Biochim. Biophys. Acta 397(): 468--477. (FBrf0027169) Moore, G.P., Sullivan, D.T. (1978). Biochemical and genetic characterization of kynurenine formamidase from Drosophila melanogaster. Biochem. Genet. 16(): 619--634. (FBrf0031070) To summarize their findings: - There are two forms of kynurenine formamidase in Drosophila melanogaster - Formamidase I (Kf1) is a homodimer with a molecular weight of 60,000, with each subunit being 34,000 - Formamidase II (Kf2) is monomeric with a molecular weight of 31,000 - While the biochemical characteristics of of formamidase I and II are distinct, their catalytic activities are similar and their amino acid compositions are virtually indistinguishable - The authors explain these data by hypothesizing the presence of two duplicate genes, which have diverged such that a dimerization motif is only present on one of them; thus, one gene encodes a non-dimerizing monomeric form (II/Kf2), and the other encodes a non-disassociating dimeric form (KfI) - Segmental aneuploid analysis identified two separate chromosomal regions whose extra dosage resulted in an elevation of formamidase activity: region 25A-27E, caused a 50% elevation in the relative amount of formamidase II; region 91B-93F caused a similar elevation in the relative amount of formamidase I Modern-day molecular-genomic analysis of the single sequence-localized gene, KFase (CG9542) shows: - Its genomic location corresponds to cytogenetic region 26D9 - It produces a single protein of 300 amino acids with a predicted molecular weight of 34,900 - Its crystal structure and biochemical characterization was reported in Han et al. 2012 (FBrf0219141), where it is described to be a monomer - BLASTn/BLASTp/tBLASTn analyses of its DNA/amino acid sequence gives only 1 significant hit (itself) in the sequenced D. melanogaster genome - Similarly, a search for D. melanogaster orthologs of the human Kynurenine formamidase/arylformamidase (AFMID) gene (using the DIOPT or HCOP tools) returns the single gene, 'KFase' - A search for D. melanogaster proteins containing the InterPro signature "Kynurenine formamidase, vertebrates/fungi-type" (IPR027519) also only returns the single gene 'KFase' Taken together, the genomic/molecular data indicate that Kynurenine formamidase is encoded by a single copy gene located at 26D9 in the (sequenced) D. melanogaster genome, and that 'KFase' (CG9542) corresponds to the 'Kf2' locus described by Moore and Sullivan. The molecular identity of 'Kf1', the proposed duplicate gene of 'KFase/Kf2' located at 91B-93F whose product dimerizes to form a functional dimer, is unknown. It's possible that this gene did exist in the D. melanogaster strain used by Moore and Sullivan but that it is absent in the sequenced genome. Alternatively, it's possible that the biochemically defined Kf1 homodimer is composed of the products of the single KFase/Kf2 gene but that these are post-translationally modified in some way, thus explaining the differences in molecular weight and biochemical characteristics. In that case, the 91B-93F region found to affect the relative amount of Kf1 activity might harbor a gene whose product regulates KFase activity.