Modulating the Copper-Sulfur Interaction in Type 1 Blue Copper Azurin by Replacing Cys112 with Nonproteinogenic Homocysteine.

摘要: The Cu–SCys interaction is known to play a dominant role in defining the type 1 (T1) blue copper center with respect both its electronic structure and electron transfer function. Despite this importance, has yet be probed by mutagenesis studies without dramatic change T1 character. We report herein replacement of conserved Cys112 azurin nonproteinogenic amino acid homocysteine. Based on absorption, paramagnetic resonance, extended X-ray absorption fine structural spectroscopic studies, variant displays typical site features. Surprisingly, instead increasing strength Cu–sulfur introduction extra methylene group, Cys112Hcy showed decrease covalent between SHcy Cu(II) when compared WT SCys–Cu(II) interaction. This likely due geometric adjustment that resulted ion moving out trigonal plane defined two histidines one Hcy closer Met121. These changes an increase reduction potential 35 mV, consistent lower Cu–S covalency. results suggest close being optimal native protein. It also demonstrates power using acids addressing important issues bioinorganic chemistry.