Ram Sanjay, Ngampasutadol Jutamas, Cox Andrew D, Blom Anna M, Lewis Lisa A, St Michael Frank, Stupak Jacek, Gulati Sunita, Rice Peter A
Division of Infectious Diseases and Immunology, University of Massachusetts Medical School, Lazare Research Building, Room 322, 364 Plantation Street, Worcester, MA 01605, USA.
Infect Immun. 2007 Aug;75(8):4071-81. doi: 10.1128/IAI.01109-06. Epub 2007 May 25.
Lipooligosaccharide (LOS) heptose (Hep) glycan substitutions influence gonococcal serum resistance. Several gonococcal strains bind the classical complement pathway inhibitor, C4b-binding protein (C4BP), via their porin (Por) molecule to escape complement-dependent killing by normal human serum (NHS). We show that the proximal glucose (Glc) on HepI is required for C4BP binding to Por1B-bearing gonococcal strains MS11 and 1291 but not to FA19 (Por1A). The presence of only the proximal Glc on HepI (lgtE mutant) permitted maximal C4BP binding to MS11 but not to 1291. Replacing 1291 lgtE Por with MS11 Por increased C4BP binding to levels that paralleled MS11 lgtE, suggesting that replacement of the Por1B molecule dictated the effects of HepI glycans on C4BP binding. The remainder of the strain background did not affect C4BP binding; replacing the Por of strain F62 with MS11 Por (F62 PorMS11) and truncating HepI mirrored the findings in the MS11 background. C4BP binding correlated with resistance to killing by NHS in most instances. F62 PorMS11 and its lgtE mutant were sensitive to NHS despite binding C4BP, secondary to kinetically overwhelming classical pathway activation and possibly increased alternative pathway activation (measured by factor Bb binding) by the F62 background. FA19 lgtF (HepI unsubstituted) resisted killing by only 10% NHS, not 50% NHS, despite binding levels of C4BP similar to those of FA19 and FA19 lgtE (both resistant to 50% serum), suggesting a role for the proximal Glc in serum resistance independently of C4BP binding. This study provides mechanistic insights into how HepI LOS substitutions affect the serum resistance of N. gonorrhoeae.
脂寡糖（LOS）庚糖（Hep）聚糖取代影响淋球菌血清抗性。几种淋球菌菌株通过其孔蛋白（Por）分子结合经典补体途径抑制剂C4b结合蛋白（C4BP），以逃避正常人血清（NHS）介导的补体依赖性杀伤。我们发现，HepI上的近端葡萄糖（Glc）是C4BP与携带Por1B的淋球菌菌株MS11和1291结合所必需的，但与FA19（Por1A）结合则不需要。仅HepI上存在近端Glc（lgtE突变体）可使C4BP与MS11最大程度结合，但不能与1291结合。用MS11的Por替换1291的lgtE Por可使C4BP结合水平增加至与MS11 lgtE相当的水平，这表明Por1B分子的替换决定了HepI聚糖对C4BP结合的影响。菌株背景的其余部分不影响C4BP结合；用MS11的Por替换菌株F62的Por（F62 PorMS11）并截断HepI反映了MS11背景中的研究结果。在大多数情况下，C4BP结合与对NHS杀伤的抗性相关。F62 PorMS11及其lgtE突变体尽管结合了C4BP，但对NHS敏感，这是由于F62背景在动力学上压倒性的经典途径激活以及可能增加的替代途径激活（通过Bb因子结合测量）所致。尽管FA19 lgtF（HepI未被取代）与FA19和FA19 lgtE（两者均对50%血清有抗性）的C4BP结合水平相似，但它仅能抵抗10%的NHS杀伤，而不能抵抗50%的NHS杀伤，这表明近端Glc在血清抗性中具有独立于C4BP结合的作用。本研究为HepI LOS取代如何影响淋病奈瑟菌的血清抗性提供了机制性见解。
