Rotational Motions of Tryptophan and Tyrosine Residues in Proteins
Proteins are flexible structures; their flexibility is crucial for biological function. The physical origin of protein flexibility has been discussed and it arises from the intrinsic flexibility of the polypeptide chain.1,2 The time scale of protein motions extends from picoseconds to several seconds depending on the process involved.3 The physiological importance of protein flexibility is well established but the functional importance of the dynamics in a given time range must still be proven. Several classes of motions can be distinguished on the basis of the element of the protein involved and of the time scale. It is likely that all of these motions can have some functional significance. It is our goal to characterize some of the motions and in particular the motions of residues. It has been proposed that correlated motions of residues occurring in the nanosecond time range can be relevant to biologically important events such as enzyme catalysis.3 However, theoretical investigations of protein motions based on molecular dynamics calculations have suggested that motions of residues occur in picoseconds.4 For example, in the molecular dynamics calculations one of the tryptophan residues in lysozyme displayed high amplitude fluctuations in few picoseconds.5 Also calculations of the rotational motions of the tyrosine residues of bovine pancreatic trypsin inhibitor (BPTI) have shown high amplitude motions in few picoseconds.6 Simulations of the motions of several other proteins have given similar results.
KeywordsRotational Motion Protein Motion Molecular Dynamic Calculation Rotational Correlation Time Protein Flexibility
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