I am making some mutants of a Calcium channel, mainly interested in a Asp residue located in S4-S5 linker. When this Asp was mutated into Glu, the channel lost its function.
Given both Asp and Glu are negatively charged, and have similiar molecular weight, I wonder why this subtle change killed the channel. Does anybody know what is the major difference between these two amino acids, in terms of biochemistry properties, strutural biology or whatever?
Thank you very much.