Aspects of cuticular sclerotization in the locust, Scistocerca gregaria, and the beetle, Tenebrio molitor

Involvement of tyrosine residues, N-terminal amino acids, and β-alanine in insect cuticular sclerotization

“…A ring-substituted histidine-dopamine adduct as well as sidechain-substituted histidine-catechol adducts have been obtained from hydrolysates of sclerotized Manduca sexta pupal cuticle (Xu et al, 1997;Kramer et al, 2001), demonstrating that histidine residues play a central role in linking acyldopamines to the cuticular proteins, and confirming that both o-quinones and p-quinone methides play roles in sclerotization. N-terminal amino groups and e-amino groups from lysine have repeatedly been suggested to be involved in sclerotization, and both histidinecontaining and lysine-containing catecholic adducts have recently been obtained from sclerotized locust cuticle by mild acid hydrolysis, indicating that free amino groups as well as imidazole groups can react with oxidized acyldopamines (Andersen and Roepstorff, 2007).…”

Quantitative determination of catecholic degradation products from insect sclerotized cuticles

“…The 3,4-dihydroxyacetophenone adducts which contain an amino acid residue linked to the a-position were suggested to be degradation products of the crosslinks formed when oxidized dehydro-NADA reacted with cuticular proteins (Andersen and Roepstorff, 2007;Andersen, 2007).…”

“…Dinitrophenylation experiments showed that in locust cuticle, which had been allowed to sclerotize for 24 h about half of the lysine residues were unavailable for dinitrophenylation, indicating that they participate in sclerotization to a limited extent (Andersen and Roepstorff, 2007). That the 3-amino group in lysine is not involved to the same extent as the N-terminal glycyl residues is probably due to the higher pK a -value of the 3-amino group.…”

“…N-terminal groups in proteins have pK a -values of about 7-8, which is significantly lower than the pK a -values of 3-amino groups from lysine (about 10-11) or phenolic groups from tyrosine (about 10-10.5) and are therefore expected to participate more readily in nucleophilic reactions than other amino groups and nearly as readily as the imidazole group in histidine (pK a about 6-7). Amino acid sequence determinations have shown that glycine is the most abundant N-terminal residue in exocuticular proteins from locusts and Tenebrio (Andersen et al, 1995(Andersen et al, , 1997, and it has been reported that N-terminal glycine amino groups rapidly disappear from locust and Tenebrio cuticle after ecdysis (Andersen and Roepstorff, 2007), indicating their involvement in sclerotization. The frequent occurrence of glycine in the N-terminal position of proteins from sclerotizable cuticles may be related to the small size of the sidechain of glycine residues, which makes it easier for the sclerotizing agent to get access to the N-terminal amino group.…”

“…Histidine-containing catecholic derivatives (I, II, IV and V, Fig. 2) have been obtained from pupal cuticle of Manduca sexta (Kerwin et al, 1999;Kramer et al, 2001) and III was obtained from adult cuticles of Schistocerca gregaria and Tenebrio molitor (Andersen and Roepstorff, 2007).…”