Assingments of tri- and tetrapeptide sequences in globular proteins to the18 kinds of local structures along helices and their propensities for specific local structures

The genetic information for local structures along helices, encoded in loca l sequences of protein chains, was statistically investigated for tri- and tetrapeptide sequences (3- and 4-letter words) using the 411 analyzed prote in chains. The 18 kinds of local structures adopted by tri- and tetrapeptid e sequences were represented 1-dimensionally by using a single helix elemen t and pairs of helix elements in parentheses, respectively. The local seque nces have propensities for none to some specific local structures along hel ices. A local structure (LS)-value is introduced for the evaluation of the normalized preference (NP)-value of a local sequence for a particular local structure. It should be emphasized that N-capping tetrapeptide sequences o f helices do not necessarily prevent helix elongation. Local structures ado pted by tetrapeptide sequences are plastic, and a particular local structur e alone helices is determined by the sequence context of helices.