title: Aggregatibacter actinomycetemcomitans leukotoxin utilizes a cholesterol recognition/amino acid consensus site for membrane association.
abstract: Aggregatibacter actinomycetemcomitans produces a repeats-in-toxin (RTX) leukotoxin (LtxA) that selectively kills human immune cells. Binding of LtxA to its β2 integrin receptor (lymphocyte function-associated antigen-1 (LFA-1)) results in the clustering of the toxin·receptor complex in lipid rafts. Clustering occurs only in the presence of LFA-1 and cholesterol, and LtxA is unable to kill cells lacking either LFA-1 or cholesterol. Here, the interaction of LtxA with cholesterol was measured using surface plasmon resonance and differential scanning calorimetry. The binding of LtxA to phospholipid bilayers increased by 4 orders of magnitude in the presence of 40% cholesterol relative to the absence of cholesterol. The affinity was specific to cholesterol and required an intact secondary structure. LtxA contains two cholesterol recognition/amino acid consensus (CRAC) sites; CRAC(336) ((333)LEEYSKR(339)) is highly conserved among RTX toxins, whereas CRAC(503) ((501)VDYLK(505)) is unique to LtxA. A peptide corresponding to CRAC(336) inhibited the ability of LtxA to kill Jurkat (Jn.9) cells. Although peptides corresponding to both CRAC(336) and CRAC(503) bind cholesterol, only CRAC(336) competitively inhibited LtxA binding to this sterol. A panel of full-length LtxA CRAC mutants demonstrated that an intact CRAC(336) site was essential for LtxA cytotoxicity. The conservation of CRAC(336) among RTX toxins suggests that this mechanism may be conserved among RTX toxins.
authors.affiliation: Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Angela C
authors.initials: AC
authors.lastname: Brown
authors.forename: Nataliya V
authors.initials: NV
authors.lastname: Balashova
authors.forename: Richard M
authors.initials: RM
authors.lastname: Epand
authors.forename: Raquel F
authors.initials: RF
authors.lastname: Epand
authors.forename: Alvina
authors.initials: A
authors.lastname: Bragin
authors.forename: Scott C
authors.initials: SC
authors.lastname: Kachlany
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Walters
authors.forename: Yurong
authors.initials: Y
authors.lastname: Du
authors.forename: Kathleen
authors.initials: K
authors.lastname: Boesze-Battaglia
authors.forename: Edward T
authors.initials: ET
authors.lastname: Lally
mesh_terms: D020816:Amino Acid Motifs; D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism; D002784:Cholesterol / Q000737:chemistry* / Q000378:metabolism; D005098:Exotoxins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry / Q000378:metabolism; D021962:Membrane Microdomains / Q000737:chemistry* / Q000378:metabolism; D015661:Pasteurellaceae / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D020349:Surface Plasmon Resonance
chemical_list: D001427:Bacterial Toxins; D005098:Exotoxins; D016169:Lymphocyte Function-Associated Antigen-1; C018579:leukotoxin; D002784:Cholesterol
keywords: Bacterial Toxins; Cholesterol; Integrins; Lipid Raft; Lipid-Protein Interaction; Microbial Pathogenesis