Structural Basis for Toughness and Flexibility in the C-terminal Passenger Domain of an Acinetobacter Trimeric Autotransporter Adhesin

Abstract

Trimeric autotransporter adhesins (TAAs) on the cell surface of Gram-negative pathogens mediate bacterial adhesion to host cells and extracellular matrix proteins. However, AtaA, a TAA in the nonpathogenic Acinetobacter sp. strain Tol 5, shows nonspecific high adhesiveness to abiotic material surfaces as well as to biotic surfaces. It consists of a passenger domain secreted by the C-terminal transmembrane anchor domain (TM), and the passenger domain contains an N-terminal head, N-terminal stalk, C-terminal head (Chead), and C-terminal stalk (Cstalk). The Chead-Cstalk-TM fragment, which is conserved in many Acinetobacter TAAs, has by itself the head-stalk-anchor architecture of a complete TAA. Here, we show the crystal structure of the Chead-Cstalk fragment, AtaA_C-terminal passenger domain (CPSD), providing the first view of several conserved TAA domains. The YadA-like head (Ylhead) of the fragment is capped by a unique structure (headCap), composed of three ␤-hairpins and a connector motif; it also contains a head insert motif (HIM1) before its last inner ␤-strand. The headCap, Ylhead, and HIM1 integrally form a stable Chead structure. Some of the major domains of the CPSD fragment are inherently flexible and provide bending sites for the fiber between segments whose toughness is ensured by topological chain exchange and hydrophobic core formation inside the trimer. Thus, although adherence assays using in-frame deletion mutants revealed that the characteristic adhesive sites of AtaA reside in its N-terminal part, the flexibility and toughness of the CPSD part provide the resilience that enables the adhesive properties of the full-length fiber across a wide range of conditions.

Empirical power laws for the radii of gyration of protein oligomers

“…The longest trimer in the data set is the Acinetobacter autotransporter adhesin (PDB entry 3wpa), which forms a remarkable particle of 310 Å in length ( Fig. 3e; Koiwai et al, 2016).…”

TheAcinetobactertrimeric autotransporter adhesin Ata controls key virulence traits ofAcinetobacter baumannii

“…In silico analyzes from sequenced Acinetobacter spp. strains revealed that species harbouring ata in their genomes span the full diversity of the genus Acinetobacter [14]. In A. baumannii ATCC 19606, the domain architecture of Ata comprises a duplicated head domain, a repetitive neck-stalk region, and membrane anchor domains (Supp.…”

“…In A. baumannii ATCC 19606, the domain architecture of Ata comprises a duplicated head domain, a repetitive neck-stalk region, and membrane anchor domains (Supp. Figure 1) [14].…”

The Secrets of Acinetobacter Secretion

“…ADP1 expressing AtaA demonstrated enhanced binding to all substrata tested when compared to the parental and empty vector controls, emphasizing the significant contribution AtaA can have on cellular adherence [72]. Subsequent structural and molecular studies on AtaA have provided the crystal structure of the C-terminal passenger domain of AtaA and identified a novel periplasmic protein, TpgA, required for anchoring AtaA to the outer membrane [73, 74]. Collectively, Acinetobacter trimeric autotransporters appear to be universally expressed by A. baumannii clinical isolates and many other Acinetobacter spp., playing a significant role in bacterial adherence and virulence.…”