Folding pattern of a protein determines its biological activity. Generally, a linear protein has no activity. Primary sequence of amino acids determines its folding pattern. Three rules governing protein folding always apply.
Peptide bond is planar and rigid.
Free rotation occurs only around alpha-Carbon Side chains of amino acids can not overlap. Certain orientations are forbidden. Two charged groups, having the same charge will not be very near one another. The sulfhydral groups of the Cysteine tend to react together to form a covalent disulfide bond. A helical conformation often adapted by a polypeptide chain and stabilized by H-bonding between every fourth amino acid.