Histidine biochemical structure

Roncone R, Monzani E, Murtas M et al (2004) Engineering peroxidase activity in myoglobin the haem cavity structure and peroxide activation in the T67R/S92D mutant and its derivative reconstituted with protohaemin-l-histidine. Biochem J 377 717-724... 

The elucidation of the X-ray structure of chymotrypsin (Ref. 1) and in a later stage of subtilisin (Ref. 2) revealed an active site with three crucial groups (Fig. 7.1)-the active serine, a neighboring histidine, and a buried aspartic acid. These three residues are frequently called the catalytic triad, and are designated here as Aspc Hisc Serc (where c indicates a catalytic residue). The identification of the location of the active-site groups and intense biochemical studies led to several mechanistic proposals for the action of serine proteases (see, for example, Refs. 1 and 2). However, it appears that without some way of translating the structural information to reaction-potential surfaces it is hard to discriminate between different alternative mechanisms. Thus it is instructive to use the procedure introduced in previous chapters and to examine the feasibility of different... 

The number of known or presumed mononuclear, non-heme iron oxygenases and related enzymes continues to grow. This is due to intensive biochemical research and especially based on sequence data derived from genome research projects i.14). For several of these enzymes structural data are available by now from protein crystallography (12-14). In many of the iron oxygenases the iron is facially bound by two histidines and one carboxylate donor, either glutamic acid or aspartic acid. Thus, the term 2-His-l-carboxylate facial triad has been introduced by L. Que Jr. for this motif (19). 

M Baedeker, G E Schulz (2002) Structures of two histidine ammonia-lyase modifications and implications for the catalytic mechanism Eur J Biochem 269(6) 1790-1797... 

Step 1 A water molecule is attracted to the zinc ion at the active site of carbonic anhydrase. The positively charged zinc ion displaces a proton from the water molecule. The displaced proton finds a new place of residence — the histidine residue. This histidine residue prt>bably aids in the removal of the proton from the water molecule, in concert wdth the action of the zinc ion. Combination of the zinc ion (Zn ) vedth the hydroxyl group does not form a complex with the structure Zn OH. The zinc atom does not change its valence (Its number of charges). Instead, the complex has the structure Zn (OH ). [Calcium ions behave similarly to zinc ions. In contrast, iron and copper ions readily change their valences when they participate in biochemical reactions.)... 

Sharma, Y. D. (1988). Genomic organization, structure and possible function of histidine-rich proteins of malaria parasites. Int. J. Biochem. 20,471-477. 

In EpiD, formation of the enethiol product has been confirmed by direct mass spectrometric and NMR analysis.A crystal structure of an EpiD mutant with a pentapeptide substrate analogue bound " and the biochemical characterization of various site-directed mutants subsequently indicated the crucial involvement of a histidine residue in the oxidation of the substrate thiol. Similar mutagenesis studies on the PPCDC activity of the E. coli CoaBC protein confirmed that this enzyme had a similar requirement, but also fingered a cysteine residue to be important in the subsequent reduction reaction. Subsequently, the AtHAL3a protein of A. thaliana was found to have PPCDC activity, and the corresponding mutants of the monofunctional protein further supported these conclusions. A crystal structure of the A. thaliana protein in which this... 

Only oxazole, of the trio, does not play any part in normal biochemical processes, though there are secondary metabolites (especially from marine organisms) which incorporate thiazole (and oxazole) units - the antibiotic cystothiazole A, from the myxobacterium Cyctobacter fuscus is an example. Imidazole occurs in the essential amino acid histidine histidines within enzymes are intimately involved in catalysis requiring proton transfers. The structurally related hormone, histamine, is a vasodilator and a major factor in allergic reactions such as hay fever. The thiazolium ring is the chemically active centre in the coenzyme derived from thiamin (vitamin B,). 

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