Towards the Development of the TPR Scaffold into Novel Biomaterials & Bioswitches.

Abstract

TetratricoPeptide Repeats or TPRs are a class of repeat proteins made up of - helices. Each repeat contains 34 amino acids that form a helix-turn-helix motif and is stabilised by short range interactions creating a non-globular fold. Tandem arrays of these repeats form stable superhelical structures. The modular nature of the TPR fold has allowed a series of consensus TPRs (CTPRs) to be designed where the number of repeat units has been varied. We have exploited the modular nature of CTPR proteins in order to create fibres via a bottom-up approach. Using Native Chemical Ligation (NCL) we have been able to trigger specific assembly of monomeric CTPR units to form extended fibrous structures up to microns in length (as viewed by TEM). This reaction proceeds at room temperature and neutral pH, with filaments observed within 12 hours. The equilibrium unfolding of CTPRs is prone to the population of partially folded states. Through studying the stability of a series of deletion mutants and using a Heteropolymer Ising model to analyse the unfolding data we have been able to design a CTPR with a conformational ‘switch’. This new CTPR was designed to populate a stable intermediate, with an exposed dimerisation interface, under certain conditions. When this new construct was analysed using 2D NMR and CD spectroscopy, it was found to selectively unfold its C-terminal -helix at a specific concentration of GuHCl. Our aim is to develop a system in which a ‘switching’ CTPR is used as a sensor that, when triggered by environmental conditions, partially unfolds and oligomerises.