The function of N^α‐acetylation of the eye‐lens crystallins

Abstract

The putative protective role of the Nu-acetyl group of proteins has been investigated. Synthetic, non-acetylated Nterminal tetrapeptides of the aA2-and 711-crystallin chains are good substrates for leucine aminopeptidase, while the acetylated ones are completely resistant. In the native, non-acetylated, y-crystallin the N terminus is not degraded by leucine aminopeptidase. Newly synthesized aA2-crystallin, in which the normally occurring N-terminal acetylation has been prevented during cell-free translation, is virtually resistant against degradation by leucine aminopeptidase. Only at extreme enzyme-substrate ratios the N-terminal methionine is removed. Although the N"-acetyl group by its very nature protects against this exopeptidase, we conclude that the group is not essential for this purpose in the native crystallins.

Comparison of N-Terminal Modifications on Neurotensin(8−13) Analogues Correlates Peptide Stability but Not Binding Affinity with in Vivo Efficacy

“…This strategy is simple, broadly applicable, and improves peptide biostability without altering the backbone and side chain functional groups necessary for full biological activity . Aminopeptidases are the major source of proteolytic activity in most tissues, and their action represents the predominant degradation pathway for peptides containing a free N-terminal amine, even in the presence of an unprotected carboxyl terminus. − Protection of the N-terminus is therefore essential to peptide stability in vivo, and methods such as N-terminal acetylation and methylation have found widespread use. ,− Additionally, our laboratory has observed that N-terminal substitution with α-azido acids, methyl groups, or hydrogen atoms substantially increased peptide biostability, hydrophobicity, and activity in various peptide models without adversely affecting other pharmacokinetic properties. − This suggests that incorporation of appropriate N-terminal modifications may have the potential to improve a greater range of peptide characteristics than currently recognized. However, direct comparisons between N-terminal modifications with respect to a variety of pharmacokinetic (PK a Abbreviations: NT, neurotensin; hNTR1, human neurotensin receptor 1; BBB, blood−brain barrier; Hlys, homolysine; ip, intraperitoneal; MALDI-TOF, matrix-assisted laser desorption ionization time-of-flight; MTBE, methyl- tert -butyl ether; Mtr, 4-methoxy-2,3,6-trimethylbenzenesulfonyl; NN, neuromedin N; NT, neurotensin; NTR, neurotensin receptor; Pbf, 2,2,4,6,7-pentamethylbenzofuran-5-sulfonyl; PK, pharmacokinetic; SAR, structure−activity relationship; X Ps , ( S )-(−)-4-(phenylmethyl)-2-oxazolidinone. ) parameters have not been reported, which is the subject of this report.…”

“…[12][13][14][15] Protection of the N-terminus is therefore essential to peptide stability in vivo, and methods such as N-terminal acetylation and methylation have found widespread use. 14,[16][17][18][19] Additionally, our laboratory has observed that N-terminal substitution with R-azido acids, methyl groups, or hydrogen atoms substantially increased peptide biostability, hydrophobicity, and activity in various peptide models without adversely affecting other pharmacokinetic properties. [20][21][22] This suggests that incorpora-tion of appropriate N-terminal modifications may have the potential to improve a greater range of peptide characteristics than currently recognized.…”

Potential Involvement of N-Terminal Acetylation in the Quantitative Regulation of the ε Subunit of Chloroplast ATP Synthase under Drought Stress

“…34) It has been reported that various metalloaminopeptidases efficiently catalyze the hydrolysis of non-acetylated proteins while N-terminalacetylated counterparts are poor substrates for these enzymes. 35,36) Based on these observations, we constructed the working hypothesis that the apparent decrease in the protein level of the non-acetylated " isoform under drought involves preferential decomposition of this isoform by metalloaminopeptidases. As a first step to test this hypothesis, we examined whether the non-acetylated " isoform is a good substrate for metalloaminopeptidases in vitro.…”

Cotranslational processing and protein turnover in eukaryotic cells

“…However, there is only limited evidence bearing on this point and not all of it is compelling. For example, attempts to establish that proteins normally N"-acetylated are more unstable without this modification have been unconvincing (Brown, 1979;Driessen et al, 1983). Nonetheless, the ubiquitous distribution of these enzymes in eukaryotic cells and their highly conserved substrate specificity (Persson et al, 1985;Sherman et al, 1986) argue for a significant role; one such possible function, directing the early routes of protein turnover, is described below.…”