How do ribosomes influence folding and misfolding of a multidomain protein during translation?

Proteins are synthesized on the ribosome as linear polypeptide chains of a specific amino
acid sequence. This polypeptide incorporates all the information needed to fold into a
three-dimensional structure which is integral to its function and, due to the vectoral nature
of synthesis, can arise prior to release. Misfolding, where a protein becomes trapped in a
conformation which causes it to misfunction, can also occur while still on the ribosome
(Plessa et al. in prep), and can be implicated in human diseases including, but not limited
to, alpha-1 antitrypsin deficiency.
To capture the process of folding this nascent polypeptide, ribosome-nascent chain
complexes (RNCs) were designed with a protein paused and tethered to the ribosome
peptidyl transferase centre (PTC) using a secretion monitor (secM) stalling sequence. In
this way, nascent chains (NCs) have been observed, using both structural and biochemical
methods, to adopt native-like structures while tethered to ribosomes, with a lengthdependent
onset of folding.
This project aims to use an integrative approach to establish what control the ribosome
exerts on a lengthening polypeptide to encourage sequential folding of a multidomain
complex and additionally prevent unfolded complexes from sampling misfolded or
aggregation-prone conformations.