Ph.D., Purdue University
Tel: (617) 552-2553
E-mail: clare.oconnor@bc.edu
Fields of Interest
Protein methylation and the repair of age-damaged proteins
Academic Profile
The goal of our research is to understandthe physiological significance of the
reactions catalyzed by a protein carboxyl methyltransferase (PCMT) with a specificity
for unusual isoaspartyl residues in proteins. Isoaspartyl residues are not incorporated
into proteins during translation, but arise spontaneously from structural changes
in proteins that accompany the aging process. The presence of an isoaspartyl
residue in a protein would be expected to put a "kink" in the protein backbone,
leading to a loss of proper protein function. Biochemical studies with the purified
PCMT and isoaspartyl-containing substrates have suggested that PCMT initiates
the structural repair of the damaged substrate, thus preventing the accumulation
of damaged proteins in cells. Judging from the nearly ubiquitous distribution
of PCMT activity in living organisms, PCMT function may be a fundamental component
of cellular protein metabolism.
Our laboratory has developed a microinjection model involving Xenopus laevis
oocytes to define the biochemical pathway initiated by carboxyl methylation.
In these experiments, oocytes are microinjected with isoaspartyl substrates
for the PCMT, and at various times after injection, substrates and metabolites
are characterized in extracts prepared from the oocytes. These experiments have
shown isoaspartyl substrates are either degraded or methylated by competing
biochemical pathways following their microinjection into Xenopus oocytes. Degradation
of one substrate, an isoaspartyl-containing variant of calmodulin, is catalyzed
directly by the 26S proteasome in an unusual pathway which does not require
ubiquitination of the isoaspartyl substrate. Thus, cells appear to have redundant
mechanisms for preventing the accumulation of potentially dysfunctional isoaspartyl-containing
proteins. Based on these results, we hypothesize that PCMT function is especially
important during physiological situations characterized by an accumulation of
abnormal proteins, such as stress and aging.
We are also using the fruitfly Drosophila melanogaster as a model for
studying the effects of PCMT overexpression and depletion in a living organism.
Drosophila makes a particularly suitable model for these studies because
of the reproducible phenotypes associated with the aging process, which occurs
over a period of about six weeks. In addition, many of the fundamental mechanisms
underlying development and neural function are conserved from Drosophila
to mammals. We have recently shown that overexpression of PCMT in adult
flies causes a dramatic extension in the adult lifespan at 29 degrees C, but
not at 25 C. The results suggest that protein repair is important in determining
the length of the lifespan. PCMT function may be particularly important at slightly
elevated temperatures, because the conformational flexibility of proteins is
greater at higher temperatures. This increase in flexibility should promote
the formation of damaged isoaspartyl residues in proteins. We are now using
P elements to generate loss-of-function mutants to determine if loss of PCMT
function has a negative effect on longevity. We are also interested in determining
the cell types that are most important in the regulation of lifespan and if
a quantitative relationship exists between the level of PCMT expression and
the length of the lifespan.
Representative Publications
O'Connor, Clare M. 2006. Protein L-isoaspartyl/D-aspartyl O- methyltransferases: Catalysts for Protein Repair. In Protein Methyltransferases, Vol. 24, The Enzymes (Eds. F. Tamanoi and S. G. Clarke),
pp. 383-431.
Bennett, E.J., Bjerregaard, J., Knapp, J.E., Chavous, D.A., Friedman, A.M., Royer, W.E., Jr., and OConnor, C.M. 2003. Catalytic implications from the Drosophila protein L-isoaspartyl methyltransferase structure and site-directed mutagenesis. Biochemistry 42: 12844–12853. (link to PubMed abstract)
Chavous, D.A., Jackson, F.R., and O'Connor, C.M. 2001. Extension of the Drosophila lifespan by overexpression of a protein repair methyltransferase. Proceedings of the National Academy of Sciences USA 98: 14814–14818. (link to PubMed abstract)Tarcsa, E., Szymanska, G., Lecker, S., O'Connor, C.M., and Goldberg, A.L. 2000. Ca2+-free calmodulin and calmodulin damaged by in vitro aging are degraded by 26S proteasomes without ubiquitination. Journal of Biological Chemistry 275: 20295–20301. (link to PubMed abstract)
Chavous, D.A., Hake, L.E., Lynch, R.J., and O'Connor, C.M. 2000. Translation of a unique transcript for protein isoaspartyl methyltransferase in haploid spermatids: Implications for protein storage and repair. Molecular Reproduction and Development 56: 139–144. (link to PubMed abstract)
Szymanska,G., Leszyk, J.D., and O'Connor, C.M. 1998. Carboxyl methylation of deamidated calmodulin increases its stability in Xenopus oocyte cytoplasm: Implications for protein repair. Journal of Biological Chemistry 273: 28516–28523. (link to PubMed abstract)
O'Connor, M.B., and O'Connor, C.M. 1998. Complex interactions of the protein L-isoaspartyl methyltransferase with calmodulin detected using the yeast two-hybrid system. Journal of Biological Chemistry 273: 12909–12913. (link to PubMed abstract)
Szymanska, G., O'Connor, M.B., and O'Connor, C.M. 1997. Construction of an epitope-tagged calmodulin useful for the analysis of calmodulin-binding proteins. Analytical Biochemistry 252: 96–105. (link to PubMed abstract)
O'Connor, M.B., Galus, A., Hartenstine, M., Magee, M., Jackson, F.R., and O'Connor,
C.M. 1997. Structural organization and developmental expression of the protein
isoaspartyl methyltransferase gene from Drosophila melanogaster. Insect
Biochemistry and Molecular Biology 27: 49–54. (link
to PubMed abstract)
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