Probing the oligomeric re-assembling of bacterial fimbriae in vitro: a small-angle X-ray scattering and analytical ultracentrifugation study

Abstract

Capsular antigen fragment 1 (Caf1) is an oligomeric protein consisting of 15 kDa monomeric subunits that are non-covalently linked through exceptionally strong and kinetically inert interactions into a linear polymer chain. It has been shown that after its thermal depolymerisation into unfolded monomeric subunits, Caf1 is able to efficiently repolymerise in vitro to reform its polymeric structure. However, little is known about the nature of the repolymerisation process. An improved understanding of this process will lead to the development of methods to better control the lengths of the repolymerised species, and ultimately, to better design of the properties of Caf1-based materials. Here we utilize small-angle X-ray scattering to estimate the size of Caf1 polymers during the first 24 h of the re-polymerisation process. Analytical ultracentrifugation measurements were also used to investigate the process post-24 h, where the rate of repolymerisation becomes considerably slower. Results show that in vitro polymerisation proceeds in a linear manner with no evidence observed for the formation of a lateral polymer network or uncontrolled aggregates. The rate of Caf1 in vitro repolymerisation was found to be concentration-dependent. Importantly, the rate of polymer growth was found to be relatively fast over the first few hours, before continuing at a dramatically slower rate. This observation is not consistent with the previously proposed step-growth mechanism of in vitro polymerisation of Caf1, where a linear increase in polymer length would be expected with time. We speculate how our observations may support the idea that the polymerisation process may be occurring at the ends of the chains with monomers adding sequentially. Our findings will contribute towards the development of new biomaterials for 3D cell culture and bio-printing.

Protein quaternary structures in solution are a mixture of multiple forms

“…Several methods can quantify mass, hence quaternary structure, and shape of a macromolecular assembly. In addition to structural methods, two traditional approaches to determine oligomeric states of proteins are analytical ultracentrifugation (AUC) 12,13 and size exclusion chromatography (SEC). The former method provides mass and stoichiometry and binding affinities by using sedimentation of macromolecules 14 , but requires large amounts of protein, is time-consuming, and requires expertise.…”

The polymer and materials science of the bacterial fimbriae Caf1

“…Experimental observations-including attempts 50 to follow the progress of polymerization by SAXS-support the idea that the in vitro polymerization of Caf1 most likely proceeds by a step-growth polymerization, 51 where monomers link into shorter oligomers, which then link into longer oligomers and eventually form longer polymer chains. This is in contrast to the in vivo polymerization of Caf1 (summarized in Fig.…”

Protein Quaternary Structures in Solution are a Mixture of Multiple forms

“…Several methods can quantify mass, hence quaternary structure, and shape of a macromolecular assembly. In addition to structural methods, two traditional approaches to determine oligomeric states of proteins are analytical ultracentrifugation (AUC) 12,13 and size exclusion chromatography (SEC). The former method provides mass and stoichiometry by using sedimentation of macromolecules 14 , but requires large amounts of protein, is time-consuming, and requires expertise.…”