| Description |
The relationship between the amino acid sequence of a protein and its three dimensional structure has long been appreciated since it was demonstrated in vitro that the information needed for a protein to fold into a functionally active structure is contained in its amino acid sequence (1). It is also known that residues in the sequence do not contribute equally in the protein folding process, since amino acid substitutions at some sites can occur without significantly altering the three dimensional structure, while substitutions at other sties can prevent the conformational folding of the protein (2,3). As a result, the relationship between amino acid sequence and the thermodynamic stability of the protein structure has been an important key in understanding which amino acids are essential in the protein folding process. One method that has been often used in trying to understand the relationships between sequence, structure and function has been to examine homologues of the protein of interest and to analyze the residues in the sequences that are conserved (2). These residues are particularly important since sequences in a family of proteins that determine structure, stability, and function should appear as conserved elements. Unfortunately, the use of sequence homologue studies are limited because it is difficult to know the roles that individual residues play in the protein folding process. However, a new development known as site directed mutagenesis has made it possible to test these roles by making mutant proteins that have single amino acid substitutions at a particular site. As a result, hypotheses that are made about the importance of a particular amino acid in the protein folding process can be checked experimentally by making site directed changes that alter specific protein residues and comparing the kinetics of unfolding with the wild type protein. |
