Disorder drives cooperative folding in a multidomain protein

Abstract

Many human proteins contain intrinsically disordered regions, and disorder in these proteins can be fundamental to their function-for example, facilitating transient but specific binding, promoting allostery, or allowing efficient posttranslational modification. SasG, a multidomain protein implicated in host colonization and biofilm formation in Staphylococcus aureus, provides another example of how disorder can play an important role. Approximately one-half of the domains in the extracellular repetitive region of SasG are intrinsically unfolded in isolation, but these E domains fold in the context of their neighboring folded G5 domains. We have previously shown that the intrinsic disorder of the E domains mediates long-range cooperativity between nonneighboring G5 domains, allowing SasG to form a long, rod-like, mechanically strong structure. Here, we show that the disorder of the E domains coupled with the remarkable stability of the interdomain interface result in cooperative folding kinetics across long distances. Formation of a small structural nucleus at one end of the molecule results in rapid structure formation over a distance of 10 nm, which is likely to be important for the maintenance of the structural integrity of SasG. Moreover, if this normal folding nucleus is disrupted by mutation, the interdomain interface is sufficiently stable to drive the folding of adjacent E and G5 domains along a parallel folding pathway, thus maintaining cooperative folding.IDP | protein folding | parallel pathways | protein engineering | cooperativity I t has been suggested that as much as 20% of the proteome may be intrinsically disordered (1), mainly manifested as intrinsically disordered regions within multidomain proteins, although a few proteins are apparently entirely disordered. Some proteins function as a consequence of disorder: for example, disordered PEVK regions of titin act as an entropic spring (2), whereas in the nuclear pore complex, disordered nucleoporins provide a thick selective barrier controlling nuclear import (3). Disorder can also play other roles: it facilitates posttranslational modification and may promote allostery (4, 5). SasG (Staphylococcus aureus surface protein G) is a cell wall-attached protein from S. aureus that promotes intercellular adhesion during the accumulation phase of biofilm formation via its C-terminal repetitive region (6-8). We previously showed that this part of SasG contains alternating E and G5 domains (Fig. 1A) and that E folds when it is N-terminal of a G5 domain. The disorder of E domains in isolation is essential for formation of a long, stiff, mechanically strong, rod-like structure (9) capable of projecting the N-terminal A domain, which is involved in host colonization (6).Here, we combine biophysical measurements, protein engineering, and simulation to show that the disorder in the E domains of SasG also promotes cooperative folding and unfolding pathways. We find that SasG domains have a highly polarized transition-state (TS) structure, where formation of a sm...

The streptococcal multidomain fibrillar adhesin CshA has an elongated polymeric architecture

“…Although many fibrillar adhesins have been identified in commensal and pathogenic bacteria, only a small number of these proteins have been subjected to detailed molecular level characterization. Examples include SasG, M protein, and the AgI/II family polypeptides (10,12,(26)(27)(28)(29)(30)(31)(32)(33). Each of these adhesins exploits a startlingly disparate molecular mechanism to facilitate the formation of fibrillar structures on the bacterial cell surface.…”

Self-Referential Encoding on Modules of Anticodon Pairs—Roots of the Biological Flow System

“…The same trend is built by the data on amino acids builders of Intrinsically Disordered segments of proteins (data from [42]). The latter is especially important for the model, indicating the role of non-structured segments of proteins in not constraining the kinds of structures that may be accepted for interactions and in offering open choices for development of structures after the interactions, besides the possibility of maintaining the disordered character even after the interactions [43,44,45]. Table 4.…”

Self-Referential Encoding on Modules of Anticodon Pairs—Roots of the Biological Flow System

“…The same trend is built by the data on amino acids builders of Intrinsically Disordered segments of proteins (data from [35]). The latter is especially important for the model, indicating the role of non-structured segments of proteins in not constraining the kinds of structures that may be accepted for interactions and in offering open choices for development of structures after the interactions, besides the possibility of maintaining the disordered character even after the interactions [36,37,38]. Table 4.…”