Asparagine and residues

Asparagine residues (and glutamine residues, see below) are sites of particular instability in peptides. As will be exemplified below, rates of degradation at asparagine residues are markedly faster (tenfold and even much more) than at aspartic acid residues. As reported, the tm values for the internal asparagine in a large number of pentapeptides ranged from 6 to 507 d under... 

An interesting correlation between tripeptide sequences and genetic mutations has been made by compilation of the number of occurrences of the tripeptide sequence Asn—B—Ser and Asn—B—Thr in protein sequence-data at present available from the literature.134 A total of 18,251 tripeptide sequences from 264 proteins was grouped by computer into the 400 possible tripeptide combinations of the 20 amino acids in which the second position was ignored. The total number of Asn—B—(Ser/Thr) sequences actually present in these proteins was 61, whereas the total number theoretically expected, on the basis of a random distribution within the sequence, would have been 102. The observed data were thus lower than expected by 4 standard deviations. On the other hand, such chemically similar tripeptides as Gin—B—(Ser/Thr), Asp—B—(Ser/Thr), and (Ser/Thr)—B—Asn occurred the number of times expected for random distribution. It was suggested that this low frequency of incidence of the Asn—B—(Ser/Thr) sequence results from a restriction of its occurrence in proteins by a process of natural selection. Any protein that acquired this tripeptide as a result of a mutation would be soon rejected, because carbohydrate would be bound to the asparagine residue and its presence would interfere with the normal metabolic function of the protein. 

Mirixins A, B, and C (Fig. 57) were isolated from an ethyl acetate extract of marine bacterium Bacillus sp., obtained from sea mud near the Arctic pole by Zhang et al. in 2004. Mirixins contain three asparagine residues and the P-amino fatty acyl side chains. Mirixins A, B and C exhibit growth inhibition with IC50 values of 0.68, 1.6 and 1.3p.g/ml, respectively against HCT-116 human colon tumor cells ... 

Erythropoietin has oligosaccharides linked to three asparagine residues and one serine residue. The structures shown are approximately to scale. See page 315 for the carbohydrate key. [Draw from IBUYpdf.]... 

A small molecular weight oligosaccharide (16) attached separately at two sites near the A-terminus of bovine rhodopsin has been examined by a combination of methylation analysis, acetolysis, and enzymic studies. This structure is identical to a proposed intermediate in the biosynthesis of complex L-asparagine-linked oligosaccharides. Three oligosaccharides have been released from bovine rhodopsin by hydrazinolysis. One of the components has an identical structure to (16) except for the absence of the L-asparagine residue, and structures [(17) and (18)] were established for the other two oligosaccharides. 

The dimers assemble by the interaction of the asparagines residues and by specific coiled-coil interactions, leading to the formation of a longitudinally growing double-stranded coiled coil. After a certain length is reached, these formed fibrils can assemble laterally to give rise to fiber bundles stabilized by electrostatic interaction between adjacent positive and negative ends. It acts as polar substituents for the further addition of any one type of peptide. CD spectroscopy. X-ray fiber diffraction, and FTIR spectroscopy confirmed the formation of linear, microscale fibers of thickness of 45 nm, 20 times the expected thickness of a coiled coil. 

Proteins are also covalently modified by specific enzymes that act on side-chain functional groups or on the N- or C-termini. More than 150 types of side-chain modifications are known fhese include glycosylafions, metiiy-lations, and acefylations, among otiiers. For insfance, a variety of carbohydrates are added to proteins, primarily at asparagine residues, and serve as recognition markers on cell surfaces. 

Automated ammo acid analysis of peptides containing asparagine (Asn) and glutamine (Gin) residues gives a peak corresponding to ammonia Why" ... 

Coagulation Factors II, III, VII, IX, X, XI, and Xlla fragments, thrombin, and plasmin are classified as serine proteases because each possesses a serine residue with neighboring histidine and asparagine residues at its enzymatically active site (Table 3). Factors II, VII, IX, and X, Protein C, Protein S, and Protein Z are dependent on the presence of vitamin K [84-80-0] for their formation as biologically functionally active procoagulant glycoproteins. 

FIGURE 9.26 The carbohydrate tnoiedes of glycoproteins may be linked to the protein via (a) serine or threonine residues (in the O-linked saccharides) or (b) asparagine residues (in the N-linked saccharides), (c) N-Linked glycoproteins are of three types high mannose, complex, and hybrid, the latter of which combines structures found in the high mannose and complex saccharides. 

Structural analysis of the two pectate lyases PelC and PelE (5, 6), demonstrated that these proteins fold in a large heHx of parallel P strands. A stack of asparagine residues parallel to the helix probably plays a role in the stabUity of this structure. Identification of the structurally conserved amino adds lead to a reaHgnment of the protein sequences (7). In addition to Erwinia extracellular pectate lyases, the multiple aHgnment indudes the Bacillus subtilis pectate lyase, Aspergillus tdger and E. carotovora pectin lyases and plant proteins. 

R. Tyler-Cross and V. Schirch, Effects of amino acid sequence, buffers and ionic strength on the rate and mechanism of deamidation of asparagine residues in small peptides, J. Biol. Chem, 266, 22549 (1991). 

Radkiewicz, J. L., H. Zipse, S. Clarke, and K. N. Houk. 1996. Acclerated Racemization of Aspartic Acid and Asparagine Residues via Succinimidine Intermediates An ab initio Theoretical Exploration of Mechanism. J. Am. Chem. Soc. 118,9148. 

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