Type III Pyridoxal 5-phosphate (PLP)-Dependent Enzyme Low Specificity D-Threonine Aldolase
Low specificity D-threonine aldolase (Low specificity D-TA, EC 220.127.116.11), encoded by dtaAS gene from Arthrobacter sp. strain DK-38, is the prototype of this subfamily. Low specificity D-TAs are fold type III PLP-dependent enzymes that catalyze the interconversion between D-threonine/D-allo-threonine and glycine plus acetaldehyde. Both PLP and divalent cations (eg. Mn2+) are required for catalytic activity. Members of this subfamily show similarity to bacterial alanine racemase (AR), which contains an N-terminal PLP-binding TIM-barrel domain and a C-terminal beta-sandwich domain. AR exists as homodimers with active sites that lie at the interface between the TIM barrel domain of one subunit and the beta-sandwich domain of the other subunit. Based on its similarity to AR, it is possible that low specificity D-TAs also form dimers in solution. Experimental data show that the monomeric form of low specificity D-TAs exhibit full catalytic activity.