Protein structure question?

Question

How does the structure of a protein affect muscle contraction, regulation of enzyme activity, or cell signaling?

Answer 1

It is due to changes in the structure of the two contractile proteins, actin and myosin in muscle that cause muscle contraction.  The two proteins interact (the "head groups" on the myosin pull the actin on either side in towards the center of the sarcomere) to cause shortening of the muscle.  

A protein's function is directly related to its structure.  The myosin must have specific areas to bind the actin and to bind ATP; each part must mesh exactly or the process would not occur.