Structural and functional characterization of aspa

Authors: Takayuki Aihara Toshiya Ito Yasuaki Yamanaka Keiichi Noguchi Masafumi Odaka Masae Sekine Hiroshi Homma Masafumi Yohda

Publish Date: 2016/04/19

Volume: 20, Issue: 4, Pages: 385-393

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Abstract

Functional and structural characterizations of pyridoxal 5′phosphateindependent aspartate racemase of the acidothermophilic archaeon Picrophilus torridus were performed Picrophilus aspartate racemase exhibited high substrate specificity to aspartic acid The optimal reaction temperature was 60 °C which is almost the same as the optimal growth temperature Reflecting the low pH in the cytosol the optimal reaction pH of Picrophilus aspartate racemase was approximately 55 However the activity at the putative cytosolic pH of 46 was approximately 6 times lower than that at the optimal pH of 55 The crystal structure of Picrophilus aspartate racemase was almost the same as that of other pyridoxal 5′phosphate independent aspartate racemases In two molecules of the dimer one molecule contained a tartaric acid molecule in the catalytic site the structure of the other molecule was relatively flexible Finally we examined the intracellular existence of damino acids Unexpectedly the proportion of daspartate to total aspartate was not very high In contrast both dproline and dalanine were observed Because Picrophilus aspartate racemase is highly specific to aspartate other amino acid racemases might exist in Picrophilus torridus

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