Abstract
We examined the effects of the site-directed mutation at the D1-Ala344 (A344G, A344V, A344D) of the Synechocystis sp. PCC6803 on the structure of the Mn-cluster using the flash-induced FTIR difference spectroscopy. Mid-frequency (1800 - 1000 cm-1) S2/S1 spectra of these mutants were distinctively different from wild-type spectrum in the carboxylate stretching region (1600 - 1300 cm-1). In addition, a negative band at 1112 cm-1 was strongly induced in A344G mutant, and amide I and II bands were significantly modified in A344V mutant. These results suggest that subtle differences of side chains of the C-terminus residue characteristically modified the coordination structure of the Mn-cluster. Furthermore, the low-frequency (650 - 350 cm-1) S2/S1 spectrum demonstrated that bands at 606/625 cm-1, assigned to a Mn-O-Mn cluster mode, were largely affected in A344G mutant, suggesting that the structure of the Mn-cluster itself is changed considerably.
