Sørensen O, Bratt T, Johnsen A H, Madsen M T, Borregaard N
Granulocyte Research Laboratory, Department of Hematology, the Finsen Centre, National University Hospital, DK-2100 Copenhagen O, Denmark.
J Biol Chem. 1999 Aug 6;274(32):22445-51. doi: 10.1074/jbc.274.32.22445.
Cathelicidins are a family of antibacterial and lipopolysaccharide-binding proteins. hCAP-18, the only human cathelicidin, is a major protein of the specific granules of human neutrophils. The plasma level of hCAP-18 is >20-fold higher than that of other specific granule proteins relative to their levels within circulating neutrophils. The aim of this study was to elucidate the background for this high plasma level of hCAP-18. Plasma was subjected to molecular sieve chromatography, and hCAP-18 was found in distinct high molecular mass fractions that coeluted with apolipoproteins A-I and B, respectively. The association of hCAP-18 with lipoproteins was validated by the cofractionation of hCAP-18 with lipoproteins using two different methods for isolation of lipoproteins from plasma. Furthermore, the level of hCAP-18 in delipidated plasma was <1% of that in normal plasma. Immunoprecipitation of very low, low, and high density lipoprotein particles with anti-apolipoprotein antibodies resulted in coprecipitation of hCAP-18. The binding of hCAP-18 to lipoproteins was mediated by the antibacterial C-terminal part of the protein. The binding of hCAP-18 to lipoproteins suggests that lipoproteins may play an important role as a reservoir of this antimicrobial protein.
cathelicidin是一类抗菌和结合脂多糖的蛋白质家族。hCAP-18是唯一的人类cathelicidin，是人类中性粒细胞特异性颗粒的主要蛋白质。相对于循环中性粒细胞内的水平，hCAP-18的血浆水平比其他特异性颗粒蛋白高20倍以上。本研究的目的是阐明hCAP-18血浆水平高的背景。对血浆进行分子筛层析，发现hCAP-18存在于分别与载脂蛋白A-I和B共洗脱的不同高分子质量组分中。通过使用两种不同方法从血浆中分离脂蛋白，使hCAP-18与脂蛋白共分级分离，验证了hCAP-18与脂蛋白的关联。此外，脱脂血浆中hCAP-18的水平不到正常血浆的1%。用抗载脂蛋白抗体对极低密度、低密度和高密度脂蛋白颗粒进行免疫沉淀，导致hCAP-18共沉淀。hCAP-18与脂蛋白的结合由该蛋白质的抗菌C末端部分介导。hCAP-18与脂蛋白的结合表明，脂蛋白可能作为这种抗菌蛋白的储存库发挥重要作用。
