> 2) In my (Organic class, we were *briefly*
> covering protein structure...and I do mean brief, like
> about 20 minutes! I had a question concerning
> Glutathione which could not be answered...maybe someone
> from the group...For those of you with Solomon's text,
> this is from prob 24.8 page 1109. Glutathione is a
> tripeptide which has glu-cys-gly, but the glu-cys bond
> is made through the gamma carbon of glu to n of cys. My
> question is: Can a peptide which has this type of
> connection still bond from the c term end of the glu and
> form a branched peptide? Does this happen often? What
> does this do to additional structure? (okay...it's more
> than one question...)
Cross-links such as you describe are important in a number oc contexts. For
instance clot formation requires the crosslinking of fibrin and is accomplished
by an enzyme called transglutaminase. (see
ID 2.3.2.13
DE PROTEIN-GLUTAMINE GAMMA-GLUTAMYLTRANSFERASE.
AN TRANSGLUTAMINASE.
AN FIBRINOLIGASE.
CA PROTEIN GLUTAMINE + ALKYLAMINE = PROTEIN N5-ALKYLGLUTAMINE + NH(3).
CF CALCIUM.
CC -!- THE GAMMA-CARBOXYMIDE GROUPS OF PEPTIDE-BOUND GLUTAMINE RESIDUES ACT
CC AS ACYL DONORS, AND THE 6-AMINO-GROUPS OF PROTEIN- AND PEPTIDE-BOUND
CC LYSINE RESIDUES ACT AS ACCEPTORS, TO GIVE INTRA- AND INTER-MOLECULAR
CC N6-(5-GLUTAMYL)LYSINE CROSSLINKS.
DR P12260 F13A_BOVIN; P00488 F13A_HUMAN; P05160 F13B_HUMAN;
DR P08587 TGLC_CAVCU; Q01841 TGLC_CHICK; P21980 TGLC_HUMAN;
DR P21981 TGLC_MOUSE; P22735 TGLK_HUMAN; P22758 TGLK_RABIT;
DR P23606 TGLK_RAT ;
Additional types of cross links occur in the bacterial cell wall, and in a
variety of cell-cell contacts in higher eukaryotes. In general, these enzymes
are cataloged under E.C. 2.3.2.x, acyltransferases
A second type of cross-link is that between the C-terminus of ubiquitin and K48
of another ubiquitin molecule. This generates a branched polymer of ubiquitin
which is attached to a target protein and tagets it for degradation. See URL
http://kdwmac.biochem.emory.edu/. The structure of this polymer has been solved
for n=4 PDB entry 1TBE.
Project anyone?
_______________________________________________________
_______________________________________________________
Keith D. Wilkinson voice (404) 727-5980
Department of Biochemistry fax (404) 727-3452
Emory University School of Medicine
Atlanta, GA 30322 e-mail genekdw@bimcore.emory.edu
_______________________________________________________