A Haemophilus influenzae IgA protease‐like protein promotes intimate interaction with human epithelial cells

Abstract

Haemophilus influenzae represents a common cause of human disease and an important source of morbidity and mortality. Disease caused by this organism begins with colonization of the upper respiratory tract. Several studies indicate that H. influenzae is capable of binding to and entering cultured human cells, properties which are potentially of relevance to the process of colonization. In the present study, we isolated an H. influenzae gene designated hap, which is associated with the capacity for in vitro attachment and entry. Analysis of the derived amino acid sequence of hap demonstrated significant homology with the serine-type IgA1 proteases expressed by H. influenzae and Neisseria gonorrhoeae. It is notable that the hap product shares the catalytic domain of the IgA1 proteases and appears to be processed and secreted in an analogous manner. We speculate that the hap gene product is an important determinant of colonization, perhaps enabling the organism to evade the local immune response and thereby persist within the respiratory tract.

Chromosomal Expression of the Haemophilus influenzae Hap Autotransporter Allows Fine-Tuned Regulation of Adhesive Potential via Inhibition of Intermolecular Autoproteolysis

“…In previous work, we established that the H. influenzae Hap autotransporter promotes adherence to cultured respiratory epithelial cells and selected extracellular matrix proteins and facilitates bacterial aggregation and microcolony formation (5,7,16). Hap adhesive activity is mediated by the surface-associated Hap S passenger domain, which also has protease activity and directs autoproteolytic cleavage of itself from the membrane-associated Hap ␤ translocator domain (6).…”

“…Derivatives of strains DB117 and Rd were grown to an optical density at 600 nm (OD 600 ) of 0.8. Sarkosyl-insoluble outer membrane proteins were isolated by the method of Carlone et al (2), and extracellular proteins were precipitated from culture supernatants with 10% trichloroacetic acid as described previously (16). Outer membrane fractions were resuspended in 25 l of 10 mM HEPES (pH 7.4) plus 25 l of 2ϫ Laemmli buffer, whereas precipitated extracellular proteins were resuspended in 10 l of 1 M Tris (pH 9.0) plus 10 l of 2ϫ Laemmli buffer.…”

“…The Hap protein is a nonpilus adhesin that was first identified based on its ability to promote intimate interaction with cultured epithelial cells (16). In addition, Hap facilitates adherence to fibronectin, laminin, and collagen IV (5) and mediates bacterial aggregation and microcolony formation, a possible precursor to biofilm formation (7).…”

Type V Protein Secretion Pathway: the Autotransporter Story

“…This protein was identified as an additional adhesin in mutants deficient in expression of HMW1 and HMW2 or Hia (466). Hap is synthesized as a 155-kDa protein which is localized to the outer membrane, but it is also associated with the production of a 110-kDa extracellular protein (the passenger domain) and a second outer membrane protein of about 45 kDa (the translocating unit).…”

Autotransported Serine Protease A of Neisseria meningitidis : an Immunogenic, Surface-Exposed Outer Membrane, and Secreted Protein

“…The characteristic structure of autotransporter proteins and the secretion mechanism have been reviewed elsewhere (15,17). Autotransporter proteins, possessing a diverse array of N-terminal "functional" domains, have been reported in many gram-negative organisms (1,2,5,6,9,10,12,13,(23)(24)(25)(29)(30)(31). Typically, these proteins exhibit virulence-associated functions, such as adhesion, cytotoxicity, serum resistance, and proteolysis (14).…”