Synthetic precursor proteins

To investigate whether bevirimat functions as a PR inhibitor, several bioassays were conducted, including a cell-free fluorometric assay using a synthetic peptide substrate of PR and experiments using a recombinant form of the Gag precursor protein Pr55Gag. Both assays showed no effect of bevirimat on PR function compared with the PR inhibitor indinavir. Indeed, bevirimat at nanomolar concentrations could inhibit the replication of HIV-1 isolates resistant to PR inhibitors. 

A number of iron-containing hydroxylases share a common reaction mechanism, in which hydroxylation of the substrate is linked to decarboxylation of OC-ketoglutarate. Many of these enzymes are involved in the modification of precursor proteins to yield the final, mature, protein. This is a process of post-synthetic modification - modification of an amino acid residue after it has been incorporated into the protein during synthesis on the ribosome (see Problem 9.3 and section 9.2.3.4). 

Proline and lysine hydroxylases are required for the post-synthetic modification of procollagen in the formation of mature, insoluble, collagen, and proline hydroxylase is also required for the post-synthetic modification of the precursor proteins of osteocalcin and the Clq component of complement. 

The recognition sequence for the enzyme within pro-GnRH/GAP has been mapped to G LRPGGKR using numerous synthetic peptide substrates 17,18). The recognition sequence thus encompasses both an "upstream" monobasic amino acid and the doublet of basic amino acids. The composition and sequence of the doublet of basic residues is important for substrate specificity, and extending the peptide sequence to more closely resemble the sequence in the precursor protein improves both kinetic constants 14). 

The second complication is that, whereas in animal tissues cellular proliferation is slow compared to the synthetis of soluble proteins, and, therefore, the synthetic of new ribosomes is n igible during an experiment lasting a few minutes, this is not so in bacteria where the mean generation time is very short. For E. ccli, for example, it is 50 min, and since in this time the ribosome content will double along with that of soluble protein, we see that in 2 min (which is the shortest time usually employed) 4 % of the ribosomal protein would be synthesized from labeled precursors—an amount which would completely obliterate the 0.1 % of transient precursor protein iidiich mi t be expected to be associated with the ribosomes. 

Cytotoxic aldehydes which cannot themselves be used clinically because of binding to proteins can be administered in the acetal-glycosidic form. The amlnated compounds (2), (R=( CH ) j NH2, R =Me, n=l-i<) have been made by acetal exchange from (1) via the m-bromides and azides, giving potential 3-glucosidase Inhibitors. The amines were resistant to enzymolysls while their synthetic precursors -... 

Eeather meal, first hydroly2ed and then oxidi2ed, produces cysteic acid [13100-82-8] an excellent precursor for taurine in cats (20). Hydroly2ed feather meal may supplement the taurine provided by other dietary animal proteins and help replace part or all of the synthetic taurine in cat food formulations with considerable cost savings. 

A number of proteins containing [3Fe-4S] centers form cubane-like clustes of the type [M,3Fe-4S] (115-120), which were prepared using this facile [3Fe-4S]/[4Fe-4S] conversion pathway. The [3Fe-4S] core present in D. gigas Fdll was the first precursor used for the synthesis of heterometal cores inside a protein matrix, and the first derivative synthesized was the [Co,3Fe-4S] core (121). Similar synthetic products have also been derived in D. africanus Fdlll (118, 119). 

---