Regulating the fate of newly-synthesized proteins
Proteins are synthesized in cells by large complex molecular machines termed ribosomes. Whilst ‘nascent proteins’ are still being made by the ribosome, they already engage with factors which ensure they fold correctly and/or are targeted to specific locations within the cell (eg. endoplasmic reticulum/secretion, mitochondria or plastids). If this process goes wrong, this can lead to production of misfolded proteins and/or the mislocalization of proteins, which is frequently associated with disease, exemplified by cystic fibrosis.
Our work focuses upon investigating how the factors which regulate these processes interact with nascent proteins on the ribosome, to ensure the each nascent protein interacts with the correct processing factors at the correct time.
We utilise information from genetic, biochemical and structural approaches to address these questions. We employ both mammalian-derived in vitro assays and yeast as a genetically-tractable model system.
Control of Factor Recruitment to the Ribosomal Exit Site
A plethora of factors are now know to be recruited to the ribosome to determine folding, processing and sub-cellular targeting of nascent chains. Many of these factors appear to bind to identical or overlapping sites close to where the nascent polypeptide chain emerges from the large ribosomal subunit (the exit site). We are trying to understand how recruitment of factors to the exit site is regulated to prevent a ‘traffic jam’ of factors leading to defective or inefficient processing of nascent chains.
N-terminal processing and ER protein translocation
We have recently found that N-terminal processing of nascent chains by Methionine aminopeptidase and N-acetyl transferases, though commonplace for cytosolic proteins, rarely occurs on secretory proteins. Moreover, we have shown that such modifications are incompatible with translocation of proteins into endoplasmic reticulum (ER), the entry point to the secretory pathway. We are currently exploring the functional significance and molecular mechanism of this inhibition to gain further insight into the cellular roles of protein N-acetylation.