The lysine side chains on the protein surface in some of the most stable crystal
ID: 90024 • Letter: T
Question
The lysine side chains on the protein surface in some of the most stable crystals of proteins, like those of carboxypeptidase A, often cannot be distinguished from alanine residues. This reflects:
A. the reactivity of the epsilon amino groups of lysine with neighboring protein molecules in the crystal compromises the crystallographic resolution
B. the intrinsically limited resolution of the crystallographic data cannot reveal aliphatic side chains like that of lysine
C. dynamic movements of amino acids can occur within the crystal, as is evidenced by the capacity of crystalline carboxypeptidase A to carry out a cleavage reaction, but in most cases these movements are more easily seen from analysis of the NMR spectrum of the protein in solution.
D. the capacity of carbons in crystalline proteins to scatter X-rays is weaker than that of nitrogens.
E. All these factors affect the analysis of protein structures by X-ray crystallography.
PLEASE EXPLAIN
Explanation / Answer
Option B
The flexible side chains are sometimes not able to diffract the X-rays. This in return, does not show any electron density spot and the amino acid can be identified as a wrong amino acid. This happens with other amino acids with side chains like glutamic acid and arginine.
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