Sandbox Reserved 334: Difference between revisions

RNase S is composed of two fragments: the small fragment, S-peptide (residues 1-20), and the large fragment, S-protein (residues 21-124)<ref name= “Original”> PMID:11015216</ref>. These fragments remain tightly bound by non-covalent interactions<ref name= “RNase1”> PMID:16415350</ref>. The only observed change in covalent structure during the conversion of RNase A to RNase S is the hydrolysis of the peptide bond between the residues 20 and 21 (REF). This complex (RNase S) conserves the catalytic activity and native conformation of uncleaved RNase A, but shows a reduced conformational stability<ref name = “RNase1” />. Two hydrophobic residues, methionine 13 and phenylalanine 8, of the S-peptide contribute significantly to the stability of RNase S,<ref name = “Original” /> while three residues (Phe 8, His 12, and Met 13) seem to be essential for the for the formation of the catalytically active RNase S<ref name= “RNase2”> PMID:8453373</ref>. It has four disulfide bonds that impose rigidity to the protein<ref name = “RNase1” />. RNase S can form either as a monomer or dimer, which have similar backbone structures except for in the hinge loop region<ref name = “RNase1” />. The dimer has a ''trans'' Asn113-Pro114 peptide bond in the hinge loop, whereas the monomer has a ''cis'' bond in this position<ref name = “RNase1” />. The RNase S dimer shows significant activity against poly(A)poly(U) sequences and single stranded RNA, similar to the enzymatic activity of RNase A<ref name = “RNase1” />.

Proteolysis of RNase S can activate oligomerization by destabilizing the native state<ref name= "RNase1" />. This occurs via the three dimensional domain-swapping mechanism<ref name="RNase1" />. In this mechanism two monomers trade structural motifs called swap domains which adopt essentially identical conformations in the monomeric and oligomeric  forms<ref name= "RNase1" />. RNase S oligomerizes by swapping C termini, which are not cut by subtilisin<ref name= "RNase1" />.