Recent advances in the understanding of trimeric autotransporter adhesins

Abstract

Adhesion is the initial step in the infection process of gram-negative bacteria. It is usually followed by the formation of biofilms that serve as a hub for further spread of the infection. Type V secretion systems engage in this process by binding to components of the extracellular matrix, which is the first step in the infection process. At the same time they provide protection from the immune system by either binding components of the innate immune system or by establishing a physical layer against aggressors. Trimeric autotransporter adhesins (TAAs) are of particular interest in this family of proteins as they possess a unique structural composition which arises from constraints during translocation. The sequence of individual domains can vary dramatically while the overall structure can be very similar to one another. This patchwork approach allows researchers to draw conclusions of the underlying function of a specific domain in a structure-based approach which underscores the importance of solving structures of yet uncharacterized TAAs and their individual domains to estimate the full extent of functions of the protein a priori. Here, we describe recent advances in understanding the translocation process of TAAs and give an overview of structural motifs that are unique to this class of proteins. The role of BpaC in the infection process of Burkholderia pseudomallei is highlighted as an exceptional example of a TAA being at the centre of infection initiation.

Adhesins of Brucella: Their Roles in the Interaction with the Host

“…This concept has changed since other factors, such as chaperones and the BAM (β-barrel Assembly Machinery) system are required for secretion of these proteins. Furthermore, more recently, it was shown that another system, the TAM (Translocation and Assembly Module) complex, is also required for the correct translocation of autotransporters into the outer membrane [ 51 , 52 , 53 ]. It was proposed that this complex spanning the periplasmic space might solve the energy problem to translocate proteins through the outer membrane [ 52 ].…”

“…Furthermore, more recently, it was shown that another system, the TAM (Translocation and Assembly Module) complex, is also required for the correct translocation of autotransporters into the outer membrane [ 51 , 52 , 53 ]. It was proposed that this complex spanning the periplasmic space might solve the energy problem to translocate proteins through the outer membrane [ 52 ]. Therefore, the current model proposes that the TAM and BAM systems would act in a concerted manner [ 51 , 54 ].…”

“…Usually, the passenger domain harbors conserved structural elements named as head, connector, and stalk domains. The combinations of these repeats result in either “lollipop structures” like YadA or as “beads-on-a-string” like BadA [ 52 ]. Although the head domains typically mediate adhesion to host targets, the stalk domains can also participate in adhesion functions.…”

Non-adaptive Evolution of Trimeric Autotransporters in Brucellaceae

“…Trimeric autotransporter adhesins are a diverse, simple, and widespread type Vc secretion pathway ( Dautin and Bernstein, 2007 ; Bernstein, 2019 ; Kiessling et al, 2020 ). TAAs are modular homotrimers with various lengths and domain complexity.…”

Data_Sheet_1.ZIP

“…Trimeric autotransporter adhesins are a diverse, simple, and widespread type Vc secretion pathway (Dautin and Bernstein, 2007;Bernstein, 2019;Kiessling et al, 2020). TAAs are modular homotrimers with various lengths and domain complexity.…”