Structure of the Lectin Regulatory Domain of the Cholesterol-Dependent Cytolysin Lectinolysin Reveals the Basis for Its Lewis Antigen Specificity

Abstract

SUMMARY The cholesterol-dependent cytolysins (CDCs) punch holes in target cell membranes through a highly regulated process. Streptococcus mitis lectinolysin (LLY) exhibits another layer of regulation with a lectin domain that enhances the pore-forming activity of the toxin. We have determined the crystal structures of the lectin domain by itself and in complex with various glycans that reveal the molecular basis for the Lewis antigen specificity of LLY. A small-angle X-ray scattering study of intact LLY reveals the molecule is flat and elongated with the lectin domain oriented so that the Lewis antigen-binding site is exposed. We suggest that the lectin domain enhances the pore-forming activity of LLY by concentrating toxin molecules at fucose-rich sites on membranes, thus promoting the formation of pre-pore oligomers on the surface of susceptible cells.

The cholesterol-dependent cytolysins pneumolysin and streptolysin O require binding to red blood cell glycans for hemolytic activity

“…The examples provided in this study are the first, to our knowledge, of a CDC targeting a glycolipid receptor, because all others have targeted protein or glycoprotein receptors. This study, along with recent studies on other streptococcal (10,45) and staphylococcal cytolysins (12), supports the emerging paradigm that receptors other than membrane lipid composition define the cellular tropism of pore-forming toxins, including CDCs.…”

Functional Dissection of Toxoplasma gondii Perforin-like Protein 1 Reveals a Dual Domain Mode of Membrane Binding for Cytolysis and Parasite Egress

“…We speculate that binding through the N-terminal domain provides another means of enhancing lytic activity by allowing recognition of more than one membrane receptor. An N-terminal lectin-binding domain in the CDC lectinolysin binds to Lewis blood group antigen on the surface of erythrocytes and is thought to enhance pore formation by concentrating the toxin at fucose-rich sites on target membranes (37,39). Although C8␥ has lectin binding activity, it is a lipocalin protein associated with C8␣ and C8␤ and does not contain a MACPF domain (53).…”

“…N-terminal domains in other MACPF proteins include a low density lipoprotein receptor A domain and thrombospondin type I domains in several complement proteins (35,36). Examples of N-terminal domains in CDCs include the lectin binding domain of lectinolysin and an N-terminal PEST-like sequence in LLO (37)(38)(39)(40)(41). Because of its unique characteristics, no obvious function for the PLP1 N-terminal domain has been proposed.…”

Perfringolysin O and related cholesterol-dependent cytolysins

“…This study utilized native ILY and two ILY mutants to examine the association of CD59 with ILY throughout the assembly process. The first mutant was locked into an early prepore state (ILY ePL ) [50], originally thought to be trapped in the monomer state on the membrane, but it has since been shown to form an early-stage sodium dodecyl sulfate (SDS)-sensitive prepore oligomer [51]). The second mutant formed an SDS-resistant late-stage prepore (ILY PL ) [52].…”

“…Some strains of S. mitis and S. pseudopneumoniae express a CDC, termed lectinolysin or plate-activating factor, which contains a fucose-binding lectin at its amino terminus that appears to enhance cytolytic activity, but its function or effect on activity remains unclear [80,81]. Interestingly, this lectin appears to preferentially bind Lewis b (Le b ) and Lewis y (Le y ) antigens [51,81,82], which are typically fetal antigens or are primarily associated with adult epithelial derived tumors [83].…”