Back to Search
Start Over
The Active Site Cysteine of Ubiquitin-Conjugating Enzymes Has a Significantly Elevated pKa: Functional Implications
- Source :
- Biochemistry. 44:16385-16391
- Publication Year :
- 2005
- Publisher :
- American Chemical Society (ACS), 2005.
-
Abstract
- Ubiquitin-conjugating enzymes (E2s or Ubcs) are essential components in the ubiquitination apparatus. These enzymes accept ubiquitin from an E1 enzyme and then, usually with the aid of an E3 enzyme, donate the ubiquitin to the target protein. The function of E2 relies critically on the chemistry of its active site cysteine residue since this residue must form a thioester bond with the carboxyl terminus of ubiquitin. Despite the plethora of structural information that is available, there has been a notable dearth of information regarding the chemical basis of E2 function. Toward filling this large void in our understanding of E2 function, we have examined the pK(a) of the active site cysteine using a combination of experimental and theoretical approaches. We find, remarkably, that the pK(a) of the active site cysteine residue is elevated by approximately 2 pH units above that of a free cysteine. We have identified residues that contribute to the increase in this pK(a). On the basis of experimental values obtained with three different E2 proteins, we believe this to be a general and important characteristic of E2 protein chemistry. Sequence comparison suggests that the electrostatic environment is maintained not through strict residue conservation but through different combinations of residues near the active site. We propose that the elevated pK(a) is a regulatory mechanism that prevents the highly exposed cysteine residue in free E2 from reacting promiscuously with electron deficient chemical moieties in the cell.
- Subjects :
- Models, Molecular
Binding Sites
Sequence Homology, Amino Acid
biology
Protein Conformation
Stereochemistry
Molecular Sequence Data
Active site
Calorimetry
Hydrogen-Ion Concentration
Ubiquitin-conjugating enzyme
Biochemistry
Residue (chemistry)
chemistry.chemical_compound
Protein structure
Ubiquitin
chemistry
Ubiquitin-Conjugating Enzymes
biology.protein
Amino Acid Sequence
Cysteine
Binding site
Cysteine metabolism
Subjects
Details
- ISSN :
- 15204995 and 00062960
- Volume :
- 44
- Database :
- OpenAIRE
- Journal :
- Biochemistry
- Accession number :
- edsair.doi.dedup.....3cb12845d4ea4359f257d7559606557c