Prolyl residues

Other interesting examples of proteases that exhibit promiscuous behavior are proline dipeptidase from Alteromonas sp. JD6.5, whose original activity is to cleave a dipeptide bond with a prolyl residue at the carboxy terminus [121, 122] and aminopeptidase P (AMPP) from E. coli, which is a prohne-specific peptidase that catalyzes the hydrolysis of N-terminal peptide bonds containing a proline residue [123, 124]. Both enzymes exhibit phosphotriesterase activity. This means that they are capable of catalyzing the reaction that does not exist in nature. It is of particular importance, since they can hydrolyze unnatural substrates - triesters of phosphoric acid and diesters of phosphonic acids - such as organophosphorus pesticides or organophosphoms warfare agents (Scheme 5.25) [125]. 

Hydroxylation of prolyl residues and some lysyl residues glycosylation of some hydroxylysyl residues... 

Mineral dust-induced ROMs contributes to pulmonary fibrosis, malignancy, hypersensitivity and emphysema (Doelman etctl., 1990 Kamp etui., 1992). The involvement of ROMs in pulmonary fibrotic reactions is indicated by the participation of PMN oxidants in the autoactivation of latent coUagenase (Weiss et al., 1985). Prolyl hydroxylase, a key enzyme in collagen fibril formation, has been shown to be dependent on the reaction of superoxide with prolyl residues (Myllyla et al., 1979). 

Once it is part of a cyclic dipeptide, the prolyl residue becomes susceptible to enantiomerization by base (see Section 7.22). The implication of the tendency of dipeptide esters to form piperazine-2,5-diones is that their amino groups cannot be left unprotonated for any length of time. The problem arises during neutralization after acidolysis of a Boc-dipeptide ester and after removal of an Fmoc group from an Fmoc-dipeptide ester by piperidine or other secondary amine. The problem is so severe with proline that a synthesis involving deprotection of Fmoc-Lys(Z)-Pro-OBzl produced only the cyclic dipeptide and no linear tripeptide. The problem surfaces in solid-phase synthesis after incorporation of the second residue of a chain that is bound to the support by a benzyl-ester type linkage. There is also the added difficulty that hydroxymethyl groups are liberated, and they can be the source of other side reactions. 

Initial attempts at producing the Thr mutant of Pro-35 were unsuccessful in producing sufficient quantities of the mutant protein for functional analysis [129], suggesting that cytochrome c is significantly more sensitive to modifications at this prolyl residue than at Pro-71. Either the Thr-35 mutant is not properly processed to mature cytochrome c, it is less thermally stable than wild-type iso-2-cytochrome c, or its functional properties are sufficiently perturbed that it cannot function adequately under physiological conditions to support yeast growth. 

This enzyme [EC 3.4.11.9] (also known as Xaa-Pro aminopeptidase, X-Pro aminopeptidase, proline amino-peptidase, and aminoacylproline aminopeptidase) catalyzes the hydrolysis of a peptide bond at the iV-terminus of a peptide provided that the iV-terminal amino acyl residue is linked to a prolyl residue by that peptide bond. The enzyme will also act on dipeptides and tripeptides with that same restriction. Either manganese or cobalt is needed as a cofactor. This enzyme appears to be a membrane-bound system in both mammalian and bacterial cells. The protein belongs to the peptidase family M24B. 

This zinc-dependent enzyme [EC 3.4.15.1] (also known as dipeptidyl carboxypeptidase I, dipeptidyl-dipeptidase A, kininase II, peptidase P, and carboxycathepsin) catalyzes the release of a C-terminal dipeptide at a neutral pH. The enzyme will also act on bradykinin. The presence of prolyl residues in angiotensin I and in bradykinin results in only single dipeptides being released due to the activity of this enzyme, a protein which belongs to the peptidase M2 family. The enzyme is a glycoprotein, generally membrane-bound, that is chloride ion-dependent. 

This enzyme [EC 3.4.14.1], also called cathepsin C and cathepsin J, catalyzes the hydrolysis of a peptide bond resulting in the release of an N-terminal dipeptide, XaaXbb-Xcc, except when Xaa is an arginyl or a lysyl residue, or Xbb or Xcc is a prolyl residue. This enzyme, a member of the peptidase family Cl, is a CF-dependent lysosomal cysteine-type peptidase. 

This manganese-dependent enzyme [EC 3.4.11.5] catalyzes the release of an N-terminal prolyl residue from a peptide. The mammalian enzyme, which is not specific for prolyl bonds, is possibly identical with cytosol amino-peptidase [EC 3.4.11.1]. 

This enzyme [EC 1.14.11.7], also known as procolla-gen proline, 2-oxoglutarate 3-dioxygenase, catalyzes the reaction of a prolyl residue in procoUagen with dioxygen and a-ketoglutarate (or, 2-oxoglutarate) to produce a irans-3-hydroxyprolyl residue in procollagen, succinate, and carbon dioxide. This reaction also requires iron ions and ascorbate. 

Systematic modification of the octapeptide sequence from cin-giotensinogen (Figure 1) was undertaken to incorporate desirable properties into the peptide. Addition of a prolyl residue to the N-termlnus Improved solubility at physiologic pH, replacement of the leucyl-leucine sequence with phenylalanyl residues Improved inhibitory properties by forty-fold, and addition of a lysyl residue to the C-termlnus Increased solubility and extended half-life in vivo. These modifications yielded the Renin Inhibitory Peptide TriP) vdiich effectively blocks renin both in primates (11) and man (1 2). 

The conformational energy calculated for a frans-L-prolyl residue when Isolated from other prolyl residues in a polypeptide chain is characterized by two minima of comparable energy occurring near vj/ - 125° (A) and ly = 325° (C), where v is the angle of rotation about the C —C bond the angle of rotation about the N —C bond is fixed at approximatly 122° by the proline ring. 

In contrast to dicots, 65-75% of the hydroxy-L-prolyl residues in the hydroxy-L-proline-rich proteins from the primary wall of four monocot species, including Zea mays (pericarp), Avena sativa (coleoptile), Iris kaempferi (pericarp), and Allium porum (pericarp), are reported to have no arabinoside residues attached.231 Of the glycosylated hydroxy-L-prolyl residues, the majority are bonded to triarabinosides, although smaller proportions of tetra-, di-, and mono-arabinosides have also been detected.231... 

There is, therefore, a distinct, structural difference between the hy-droxy-L-proline-rich glycoproteins of dicots and monocots. In monocots, the degree of polymerization of arabinosides attached to hydroxy-L-prolyl residues is lower, and far fewer hydroxy-L-prolyl residues are glycosylated than in dicots. 

Hydroxylation of prolyl residues of pro-a-chains of collagen by prolyl hydroxylase. 

If, for example, there is a peptidyl-proline bond in the denatured state that has an equilibrium constant ATiso (= [DdJ/[DfranJ), then the equilibrium constant for unfolding will be increased by a factor of 1 + fiso, since [DdJ] + [D,ra J = (1 + iSo)[Dfran.j] Since Kiso is generally in the range of 0.05 to 0.2, this is a small factor if there are just three or four trans-peptidyl prolines in the native state. But if N contains a ds-peptidyl-proline bond, then this leads to very large factors (5 to 20) for each such prolyl residue. 

Figure 14 Plot of the conformations of 326 prolyl residues (from X-ray structures of proteins) in the conventional (,< 0 map.

Fig. 3.3 The structure of the N-terminal SH3 domain of Grb2 bound to a proline-rich Sos peptide has been determined by NMR.29.30 The structure of the Gbr2 N-terminal SH3 domain, compiexed with a 10-residue peptide, comprising residues 1134-1144 (VPPPVPPRRR-NHz) of Sos, is shown. The prolyl residues, P2, P3, P6, and P7, which interact with the SH3 domain of Grb2 are marked. (The ribbon model was reproduced with permission of the authors and J. Mol. Biol, from data in ref. 30, available In databanks.) A variation of this scheme is the recognition of a proline-rich sequence (APTMPPPLPP) in the GAP protein for Rho by the SH3-domain of the cytosolic c-Abi tyrosine kinase. i This interaction couples the Rho/GAP tightly to this cytosolic tyrosine kinase and brings the momomeric G protein, Rho, under the control of phosphorylation by the kinase.

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