The full length of mature staphylokinase
mRNA is 489bp. The first 27
amino acids code for a signal
peptide which is cleaved off in the mature protein (mSak). There is little or no homology between the
primary structure of Sak and other plasminogen activators. The natural variants of Sak are Sak42D, SakφC and SakSTAR. These variants have four
nucleotide differences in the coding region with one
silent mutation. The affected codons are amino acids 38, 61, 63 and 70 in the full length staphylokinase. Amino acid 38 is
lysine, amino acid 61 is
serine in SaKSTAR,
glycine in SakφC, and
arginine in Sak42D. Amino acid 63 is glycine in SakSTAR and SakφC, but arginine in Sak42D. SakSTAR and SakφC amino acid 70 is
histidine, whereas it is arginine in Sak42D. The mature structure of staphylokinase consists of 163 amino acids, and it is elongated in shape. Sak contains two folded
domains which are of similar size. The distance from the center of gravity between the two domains is 3.7 nm. When in solution, this position varies between the two domains suggesting a flexible
dumbbell shape. ==See also==