Type V secretion: From biogenesis to biotechnology

Abstract

The two membranes of Gram-negative bacteria contain protein machines that have a general function in their assembly. To interact with the extra-cellular milieu, Gram-negatives target proteins to their cell surface and beyond. Many specialized secretion systems have evolved with dedicated translocation machines that either span the entire cell envelope or localize to the outer membrane. The latter act in concert with inner-membrane transport systems (i.e. Sec or Tat). Secretion via the Type V secretion system follows a two-step mechanism that appears relatively simple. Proteins secreted via this pathway are important for the Gram-negative life-style, either as virulence factors for pathogens or by contributing to the survival of non-invasive environmental species. Furthermore, this system appears well suited for the secretion of biotechnologically relevant proteins. In this review we focus on the biogenesis and application of two Type V subtypes, the autotransporters and two-partner secretion (TPS) systems. For translocation across the outer membrane the autotransporters require the assistance of the Bam complex that also plays a generic role in the assembly of outer membrane proteins. The TPS systems do use a dedicated translocator, but this protein shows resemblance to BamA, the major component of the Bam complex. Interestingly, both the mechanistic and more applied studies on these systems have provided a better understanding of the secretion mechanism and the biogenesis of outer membrane proteins. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.

Antibodies against In Vivo -Expressed Antigens Are Sufficient To Protect against Lethal Aerosol Infection with Burkholderia mallei and Burkholderia pseudomallei

“…Given their important roles in pathogenicity, overall structure, and cellular location at the host-pathogen interface, autotransporter proteins (ATs) represent excellent targets for developing countermeasures (65)(66)(67)(68)(69)(70)(71)(72)(73)(74). These molecules form one of the largest families of virulence factors in Gram-negative bacteria and contribute a wide range of phenotypes, such as serum resistance, lipolytic activity, biofilms, and host cell adhesion (75)(76)(77)(78)(79).…”

“…Autotransporters also share 4 structural features: a signal sequence directing the protein to cell membranes for secretion, an N-terminal passenger domain that specifies the biological function, a C-terminal transporter domain anchoring the AT to the outer membrane, and a helical linker region of ϳ40 amino acids that connects the passenger and transporter domains. Based on the structure of the transporter domain, ATs can be classified as oligomeric or conventional (65)(66)(67)(68)(69)(70)(71)(72)(73)(74)80). Oligomeric ATs have a short C terminus of ϳ70 amino acids that forms 4 antiparallel ␤-strands and are produced as trimers.…”

Bacterial killing via a type IV secretion system

“…These interactions have driven the evolution of several mechanisms by which they quickly deploy proteinaceous and nucleic acid effectors that manipulate the behaviour of the target organism, often resulting in growth inhibition or death [1][2][3][4][5][6] . Distinct among these mechanisms are the type III, type IV and type VI secretion systems (T3SS, T4SS and T6SS, respectively) that are all capable of transferring proteins, and in the case of the T4SS, protein-DNA complexes, directly into neighbouring cells in a contact-dependent manner [1][2][3] .…”

The Polypeptide Transport-associated (POTRA) Domains of TpsB Transporters Determine the System Specificity of Two-partner Secretion Systems

“…Proteins of the type V secretion pathway of Gram-negative bacteria cross the cell envelope consisting of the inner membrane, the peptidoglycan-containing periplasmic space, and the outer membrane in a series of consecutive steps (1). Within the type V secretion pathway, the two-partner secretion (TPS) 4 systems form a distinct subclass (1,2).…”

“…Within the type V secretion pathway, the two-partner secretion (TPS) 4 systems form a distinct subclass (1,2). TPS systems comprise a secreted TpsA protein and an outer membrane-embedded TpsB transporter.…”