N-Phosphoryl amino acids

Because of their abilities in both peptide and nucleic acid oligomerization, N-phosphoryl amino acids could have played an important role in prebiotic chemistry on condition that a plausible pathway of synthesis of these compounds is made available. 

The phosphorothioic triamide (79) (R = H) exhibits ambident reactivity and when alkylated yields the pentacoordinated 5-derivatives (80), but when acylated affords (79) (R = PhCO or EtCO). The N io O rearrangement of the N-phosphorylated amino acid esters (81) to (82) proceeds 10-40 times faster in the presence of imidazole than in its absence. In a warm alcohol solution ester... 

Enzyme preparations from liver or microbial sources were reported to show rather high substrate specificity [76] for the natural phosphorylated acceptor d-(18) but, at much reduced reaction rates, offer a rather broad substrate tolerance for polar, short-chain aldehydes [77-79]. Simple aliphatic or aromatic aldehydes are not converted. Therefore, the aldolase from Escherichia coli has been mutated for improved acceptance of nonphosphorylated and enantiomeric substrates toward facilitated enzymatic syntheses ofboth d- and t-sugars [80,81]. High stereoselectivity of the wild-type enzyme has been utilized in the preparation of compounds (23) / (24) and in a two-step enzymatic synthesis of (22), the N-terminal amino acid portion of nikkomycin antibiotics (Figure 10.12) [82]. 

Fig. 5. Primary structure and site of phosphorylation of k-CN A-1P, and the site of cleavage by chymosin (V). The N-terminal amino acid is pyroglutamate (Eigel et al., 1984 Thompson et al., 1985).

The possibilities of N-(dialkylphosphoryl)amino acids for the prebiotic syntheses of peptides and polynucleotides have been studied in a series of papers [24,116-122], However, it must be emphasized that the phosphoryl group does not behave as an amino-activating group, the hydrolysis of which would be coupled to peptide bond formation. Actually, further peptide elongation requires the subsequent hydrolysis of the N-terminal phosphoryl group of the ligated product. In the presence of an amino acid ester, dipeptide esters 16 with an unreacted N-phosphoryl protection are formed, support-... 

In relation with the unique reactivity of N-(dialkylphosphoryl)amino acids mentioned above (see Sect. 3.2.3), a conversion of the carboxylic-phosphoric mixed anhydride 18f (R1 = R2 = alkyl) would provide an appealing pathway for the formation of the AT-phosphorylated derivatives. The reaction of NCAs might have then allowed a pathway for the formation of these versatile intermediates that can be useful for nucleotide ligation. 

A hydrophobic 10 kDa protein is also associated with PS II preparations [14], but its function is obscure. The protein is phosphorylated by a membrane-bound protein kinase [15] and the identity of this phosphoprotein has been the subject of much speculation [16]. It is clearly not the 9 kDa polypeptide of Cyt 6-559 or the 8 kDa proteolipid subunit of ATP synthase as shown by N-terminal amino acid sequence [14]. 

Do you know the amino acid sequence (e.g., from cDNA cloning) and do you have purified protein Then you can determine the MW of the protein via MALDI-TOF and compare to the MW calculated from the cDNA sequence. If the MW are identical, the primary structure of your protein is correct. Deviations are evidence of modifications (e.g., phosphorylations, glycosylations, point mutations). With smaller proteins, the acetylation of the N-terminal amino acid becomes apparent in the MALDI-TOF. You determine the position of a modification by cutting the protein into peptides, measuring the MW of the individual peptides, and comparing to the MW predicted from the sequence. 

The phosducin polypeptide chmn, of some 240 amino acids, is folded into two domains (Figure 13.16). The N-terminal domain is mostly a-helical and appears to be quite flexible since only a weak electron density is obtained in the structure determination. The actual path of the polypeptide chain from the end of helix to the beginning of helix Ba is tentative due to slight disorder. This region is close to serine 73 at the beginning of Ba, which also becomes disordered on phosphorylation. 

Landry, J., Lambert, H., Zhou, M., Lavoie, J.N., Hickey, E., Weber, L.A., Anderson, C.W. (1992). Human hsp27 is phosphorylated at serines 78 and 82 by heat shock and mitogen activated kinases that recognize the same amino acid motif as S6 kinase 11. J. Biol. 267, 794-803. 

Posttranslational modifications of S-layer proteins include cleavage of N- or C-terminal fragments, glycosylation, and phosphorylation of amino acid residues. 

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