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Homocysteine thiolactone affects protein ubiquitination in yeast

100%
Bretes E., Zimny J.
Acta Biochimica Polonica
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2013
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vol. 60
|
issue 3
485-488
EN
The formation of homocysteine thiolactone (HcyTl) from homocysteine occurs in all examined so far organisms including bacteria, yeast, and humans. Protein N-homocysteinylation at the ε-amino group of lysine is an adverse result of HcyTl accumulation. Since tagging of proteins by ubiquitination before their proteasomal degradation takes place at the same residue, we wondered how N-homocysteinylation may affect the ubiquitination of proteins. We used different yeast strains carrying mutations in genes involved in the homocysteine metabolism. We found positive correlation between the concentration of endogenous HcyTl and the concentration of ubiquitinated proteins. This suggests that N-homocysteinylation of proteins apparently does not preclude but rather promotes their decomposition.
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Hint2, the mitochondrial nucleoside 5'-phosphoramidate hydrolase; properties of the homogeneous protein from sheep (Ovis aries) liver

61%
Bretes E., Wojdyła-Mamoń A. M., Kowalska J., Jemielity J., Kaczmarek R., Baraniak J., Guranowski A.
Acta Biochimica Polonica
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2013
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vol. 60
|
issue 2
249-254
EN
Adenosine 5'-phosphoramidate (NH2-pA) is a rare natural nucleotide and its biochemistry and biological functions are poorly recognized. All organisms have proteins that may be involved in the catabolism of NH2-pA. They are members of the HIT protein family and catalyze hydrolytic splitting of NH2-pA to 5'-AMP and ammonia. At least five HIT proteins have been identified in mammals; however, the enzymatic and molecular properties of only Fhit and Hint1 have been comprehensively studied. Our study focuses on the Hint2 protein purified by a simple procedure to homogeneity from sheep liver mitochondrial fraction (OaHint2). Hint1 protein was also prepared from sheep liver (OaHint1) and the molecular and kinetic properties of the two proteins compared. Both function as homodimers and behave as nucleoside 5'-phosphoramidate hydrolases. The molecular mass of the OaHint2 monomer is 16 kDa and that of the OaHint1 monomer 14.9 kDa. Among potential substrates studied, NH2-pA appeared to be the best; the Km and kcat values estimated for this compound are 6.6 μM and 68.3 s-1, and 1.5 μM and 11.0 s-1 per natively functioning dimer of OaHint2 and OaHint1, respectively. Studies of the rates of hydrolysis of different NH2-pA derivatives show that Hint2 is more specific towards compounds with a P-N bond than Hint1. The thermostability of these two proteins is also compared.
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