Author/Editor		Andersen, Gorm; Andersen, Birgit; Dobritzsch, Doreen; Schnackerz, Klaus D; Piškur, Jure
Title		A gene duplication led to specialized gamma-aminobutyrate and beta-alanine aminotransferase in yeast
Type		članek
Source		FEBS J purification/metabolism
Vol. and No.		Letnik 274, št. 7
Publication year		2007
Volume		str. 1804-17
Language		eng
Abstract		In humans, beta-alanine (BAL) and the neurotransmitter gamma-aminobutyrate (GABA) are transaminated by a single aminotransferase enzyme. Apparently, yeast originally also had a single enzyme, but the corresponding gene was duplicated in the Saccharomyces kluyveri lineage. SkUGA1 encodes a homologue of Saccharomyces cerevisiae GABA aminotransferase, and SkPYD4 encodes an enzyme involved in both BAL and GABA transamination. SkPYD4 and SkUGA1 as well as S. cerevisiae UGA1 and Schizosaccharomyces pombe UGA1 were subcloned, over-expressed and purified. One discontinuous and two continuous coupled assays were used to characterize the substrate specificity and kinetic parameters of the four enzymes. It was found that the cofactor pyridoxal 5'-phosphate is needed for enzymatic activity and alpha-ketoglutarate, and not pyruvate, as the amino group acceptor. SkPyd4p preferentially uses BAL as the amino group donor (V(max)/K(m)=0.78 U x mg(-1) x mm(-1)), but can also use GABA (V(max)/K(m)=0.42 U x mg(-1) x mm(-1)), while SkUga1p only uses GABA (V(max)/K(m)=4.01 U x mg(-1) x mm(-1)). SpUga1p and ScUga1p transaminate only GABA and not BAL. While mammals degrade BAL and GABA with only one enzyme, but in different tissues, S. kluyveri and related yeasts have two different genes/enzymes to apparently 'distinguish' between the two reactions in a single cell. It is likely that upon duplication approximately 200 million years ago, a specialized Uga1p evolved into a 'novel' transaminase enzyme with broader substrate specificity.
Descriptors		CATALYSIS CLONING, MOLECULAR ENZYME STABILITY FUNGAL PROTEINS GENOTYPE HYDROGEN-ION CONCENTRATION KINETICS MOLECULAR SEQUENCE DATA MUTATION PHENOTYPE PHYLOGENY SACCHAROMYCES CEREVISIAE SCHIZOSACCHAROMYCES SPECTRUM ANALYSIS SUBSTRATE SPECIFICITY YEASTS BETA-ALANINE