Protein Carboxylation

Murray, Jr., E. D. and Clarke, S., Synthetic peptide substrates for the erythrocyte protein carboxyl methyltransferase, J. Biol. Chem., 259, 10722, 1984. 

Figure 1.71 Cystamine may be used to label protein carboxylate groups using the water-soluble carbodiimide EDC.

The following protocol using the carbodiimide EDC is an efficient way of modifying protein carboxylates with diamines to either increase the amount of amines present for further conjugation or to create a cationized protein having an increased net charge (Figure 1.90). Note that... 

Johnson B.A., Langmark E.L., and Aswad D.W. (1987), Partial repair of deamidation damaged calmodulin by protein carboxyl methyltransferase, J. Biol. Chem. 262, 12283-12287. 

Currently, only a handful of examples of unique protein carboxylate-zinc interactions are available in the Brookhaven Protein Data Bank. Each of these entries, however, displays syn coordination stereochemistry, and two are bidentate (Christianson and Alexander, 1989) (Fig. 5). Other protein structures have been reported with iyw-oriented car-boxylate-zinc interactions, but full coordinate sets are not yet available [e.g., DNA polymerase (Ollis etal., 1985) and alkaline phosphatase (Kim and Wyckoff, 1989)]. A survey of all protein-metal ion interactions reveals that jyw-carboxylate—metal ion stereochemistry is preferred (Chakrabarti, 1990a). It is been suggested that potent zinc enzyme inhibition arises from syn-oriented interactions between inhibitor carboxylates and active-site zinc ions (Christianson and Lipscomb, 1988a see also Monzingo and Matthews, 1984), and the structures of such interactions may sample the reaction coordinate for enzymatic catalysis in certain systems (Christianson and Lipscomb, 1987). 

Antisera to cloxacillin/oxacillin/dicloxacillin and cefuroxime were also produced by similar procedures and successfully utilized in methods for the detection of these antibiotics in milk (34). Unfortunately, a number of other -lactams including aminopenicillins and some cephalosporins were not amenable to this mixed anhydride procedure. Thus, a carrier protein derivatization procedure was used to allow cross-linking of cephalosporins, such as cephataxime that has an acetoxy side chain, to ovalbumin. Because acetoxy groups react readily with the heterocyclic nitrogen atoms, the latter were introduced into ovalbumin through the carbodiimide-mediated derivatization of protein carboxyl groups with amino-methylpyridine (34). 

Fig. 3. Proposed reaction cycle for urease. For urea, R = —NH2. Step 1 urea is activated toward nucleophilic attack by O coordination to a nickel ion the =N+H2 is stabilized by interaction with a protein carboxylate. Step 2 nucleophilic attack by a hydroxide ion, coordinated to the second nickel, to form a tetrahedral intermediate. Step 3 breakdown of the tetrahedral intermediate to form a coordinated carbamate ion. Step 4 hydrolysis releases carbamate ion, the initial product of urease on urea. Reproduced, with permission, from Ref. 34.

Aswad DW. Stoichiometric methylation of porcine adrenocorticotropin by protein carboxyl methyltransferase requires deamidation of asparagine 25. Evidence for methylation at the alpha-carboxyl group of atypical L-isoaspartyl residues. J Biol Chem 1984 259 10714-10721. 

Covalent Attachment of Amino Acids to "Protein Carboxyl Groups... 

Pig. 5.9 Mechanism proposed for formation of a covalent bond between a heme methyl and a protein carboxyl group. A similar sequence must occur again to form the second heme-protein ester link in the mammalian peroxidases. In the heme structure, V stands for -CH=CH2 and P for... 

A third group of OMTs are the protein carboxyl MTs, whose molecular mass is approximately 27 kDa 43 These proteins are found in almost all organisms, and they serve to repair damaged proteins. In plants, they have been shown to be important during stress and in seed viability.14. Their sequences are related to the animal glycine N-methyltransferases (NMTs) and die RNA/DNA MTs. Furthermore, the plant protein carboxyl MTs share no similarity to the other plant MTs involved in specialized metabolism. The enzyme that methylates a carboxyl functionality of Mg-protoporphyrin IX to produce a methylester constitutes a fourth type of plant OMT. This chloroplastic protein, whose mature form has a molecular mass of 31 kDa, is related to MTs with similar functions from photosynthetic bacteria, but is not closely related to any other plant OMTs.6... 

A number of proteins such as histones, cytochrome c and certain flagellar proteins are found to contain methylated amino acids (19). Three different methylases have been characterized and all require S-adenosylmethionine (SAM) as the methyl donor (20-23). Protein methylase I (SAM-protein arginine methyl transferase) methylates the guanidine side chain of arginine residue protein methylase II (SAM-protein carboxyl methyltransferase) transfers methyl groups only to 8- and y-carboxyl groups in the peptide chain. Carboxyl groups in the a position cannot serve as acceptors. Protein methylase III (SAM-protein lysine... 

The carbohydrate-binding sites of WGA are probably situated at the surface of the protein molecule. The pH dependences of association constants for lectin-chitotriose binding indicate that an ionizable group, pK = 3.9, is probably involved in complex-formation.494,504 This observation is especially noteworthy, inasmuch as protein carboxyl... 

The active site consists of two iron atoms, roughly 3.25-3.5 A apart, bound to the protein ligand by live histidine side-chain residues. In the reduced deoxy form the core is asymmetric, having one 5-coordinate and one 6-coordinate iron atom. Two protein carboxylate units and one hydroxo group derived from water are bridged across the iron atoms as shown in Fig. 17-E-9. 

Lycksell, P. O., Ingemarson, R., Davis, R., Gr%oslund, A., and Thelander, L., 1994, H NMR studies of mouse ribonucleotide reductaseoThe R2 protein carboxyl-terminal tail, essential for subunit interaction, is highly flexible but becomes rigid in the presence of protein Rl. Biochemistry 33 2838n2842. 

Clarke, S., Vogel, J.P., Deschenes, R.J., and Stock, J. (1988). Posttranslational modification of the Ha-ras oncogene protein evidence for a third class of protein carboxyl methyltrans-ferases. Proc Natl Acad Sci USA 85 4643 647. 

Stephenson, R.C., and Clarke, S. (1990). Identification of a C-terminal protein carboxyl methyltransferase in rat liver membranes utilizing a synthetic farnesyl cysteine-containing peptide substrate. J Biol Chem 265 16248-16254. 

Volker, C., et al. (1991). Effects of farnesylcysteine analogs on protein carboxyl methyla-tion and signal transduction. J Biol Chem 266 21515-21522. 

---