Zhang Xianwei, Bajic Goran, Andersen Gregers R, Christiansen Stig Hill, Vorup-Jensen Thomas
Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark.
Department of Molecular Biology and Genetics, Aarhus University, DK-8000 Aarhus C, Denmark.
Biochim Biophys Acta. 2016 May;1864(5):471-8. doi: 10.1016/j.bbapap.2016.02.013. Epub 2016 Feb 11.
As a broad-spectrum anti-microbial peptide, LL-37 plays an important role in the innate immune system. A series of previous reports implicates LL-37 as an activator of various cell surface receptor-mediated functions, including chemotaxis in integrin CD11b/CD18 (Mac-1)-expressing cells. However, evidence is scarce concerning the direct binding of LL-37 to these receptors and investigations on the associated binding kinetics is lacking. Mac-1, a member of the β2 integrin family, is mainly expressed in myeloid leukocytes. Its critical functions include phagocytosis of complement-opsonized pathogens. Here, we report on interactions of LL-37 and its fragment FK-13 with the ligand-binding domain of Mac-1, the α-chain I domain. LL-37 bound the I-domain with an affinity comparable to the complement fragment C3d, one of the strongest known ligands for Mac-1. In cell adhesion assays both LL-37 and FK-13 supported binding by Mac-1 expressing cells, however, with LL-37-coupled surfaces supporting stronger cell adhesion than FK-13. Likewise, in phagocytosis assays with primary human monocytes both LL-37 and FK-13 enhanced uptake of particles coupled with these ligands but with a tendency towards a stronger uptake by LL-37.
作为一种广谱抗菌肽，LL-37在先天免疫系统中发挥着重要作用。此前的一系列报告表明，LL-37是多种细胞表面受体介导功能的激活剂，包括在表达整合素CD11b/CD18（Mac-1）的细胞中的趋化作用。然而，关于LL-37与这些受体直接结合的证据很少，并且缺乏对相关结合动力学的研究。Mac-1是β2整合素家族的成员，主要在髓系白细胞中表达。其关键功能包括吞噬补体调理的病原体。在此，我们报告了LL-37及其片段FK-13与Mac-1的配体结合域α链I结构域的相互作用。LL-37与I结构域的结合亲和力与补体片段C3d相当，C3d是已知最强的Mac-1配体之一。在细胞黏附试验中，LL-37和FK-13都支持表达Mac-1的细胞的黏附，然而，与FK-13相比，LL-37偶联的表面支持更强的细胞黏附。同样，在原代人单核细胞的吞噬试验中，LL-37和FK-13都增强了与这些配体偶联的颗粒的摄取，但LL-37的摄取倾向更强。
