Subunit dissociation and stability alteration of D-hydantoinase deleted at the terminal amino acid residue

Two variants of d-hydantoinase (HYD), created by deletion of one amino acid residue of at either the N- or C-terminus, were expressed in Escherichia coli and purified by two-step chromatography. Compared with HYD, HYDc1 with the C-terminal Arg deletion retained 43% activity, while HYDn1 with the N-terminal Ser deletion had no activity using dl-Hydantoin as substrate. Based on HYD dimer with a molecular weight of 103 kDa, HYDc1 is a monomer of 52 kDa and HYDn1 is a mixture of dimer and monomer. Moreover, HYDc1 displayed higher pH stability and lower thermal stability compared to HYD. In addition, the secondary and tertiary structures of HYDc1 were not significantly changed in contrast to the ones of HYDn1. All data imply that the C-terminal Arg of the HYD is crucial for homodimeric architecture of the enzyme, but non-essential for catalysis, while the N-terminal Ser is required for both conformation and catalysis of the enzyme.