title: Two domains with amino-acid sequence similarity are required for dihydroneopterin aldolase function in the multifunctional folic acid synthesis Fas protein of Pneumocystis carinii.
abstract: The folic acid synthesized gene (fas) of Pneumocystis carinii (Pc) codes for a multifunctional enzyme (Fas) known to catalyse three consecutive steps leading to the production of dihydropteroate in the de novo folate synthesis pathway. Previously, we predicted that a domain, designated FasB (amino acids (aa) 161-280), of the 740-aa multifunctional protein contains the first of the three enzyme activities in the pathway, namely dihydroneopterin aldolase (DHNA), since it shares 23% aa identity with the DHNA of Streptococcus pneumoniae (Sp). We now extend these findings to show that a second domain, FasA (aa 39-160), whose function was previously unknown, shares 27% sequence identity with the adjacent FasB domain, indicative of functional similarity. FasA is also 18% identical with the DHNA from Sp. Recombinant baculoviruses were constructed which directed the production of either FasA, FasB or FasAB polypeptide species in cultured Spodoptera frugiperda (SF9) insect cells. No DHNA activity is associated with either fasA or fasB when produced as single domains in the insect-baculovirus system. However, DHNA activity was detected in SF9 extracts containing the overproduced FasAB polypeptide. The results of aa sequence alignments and expression studies suggest that FasA and FasB may be two subunits of the DHNA enzyme moiety within the multifunctional Fas protein of Pc. An alternative interpretation of the results is also discussed.
authors.affiliation: Structural Biology Group, Wellcome Research Laboratories, Beckenham, Kent, UK.
authors.forename: F
authors.initials: F
authors.lastname: Volpe
authors.forename: S P
authors.initials: SP
authors.lastname: Ballantine
authors.forename: C J
authors.initials: CJ
authors.lastname: Delves
mesh_terms: D000446:Aldehyde-Lyases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D017931:DNA Primers; D005492:Folic Acid / Q000096:biosynthesis; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D007700:Kinetics; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D011010:Pneumocystis / Q000201:enzymology* / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D018411:Spodoptera; D013296:Streptococcus pneumoniae / Q000235:genetics; D014162:Transfection; D019014:fas Receptor
chemical_list: D000954:Antigens, Surface; D017931:DNA Primers; C094979:FasA protein, Pneumocystis; C094980:FasB protein, Pneumocystis; D005656:Fungal Proteins; D011994:Recombinant Proteins; D019014:fas Receptor; D005492:Folic Acid; D000446:Aldehyde-Lyases; C020044:dihydroneopterin aldolase