Y. Hirako et al., DEMONSTRATION OF THE MOLECULAR SHAPE OF BP180, A 180-KDA BULLOUS PEMPHIGOID ANTIGEN AND ITS POTENTIAL FOR TRIMER FORMATION, The Journal of biological chemistry, 271(23), 1996, pp. 13739-13745
The 180-kDa bullous pemphigoid antigen (BP180) is a hemidesmosomal tra
nsmembrane glycoprotein comprising interrupted collagen domains in its
extracellular part, BP180 is also termed type XVII collagen, But the
question of whether it actually takes a collagen-like triple helical c
onformation in. vivo has remained unanswered, Using a monoclonal antib
ody, we found that a sub-population of BP180 localizes at the lateral
surfaces of corneal basal cells and cultured cells, in addition to the
basal surface, This subpopulation of BP180 could be solubilized by 0.
5% Triton X-100 and, among examined cell lines, was found to be most a
bundant in BMGE+H, a bovine mammary gland epithelial cell line, The Tr
iton soluble fraction of BMGE+H cells was used for characterization, O
n sucrose gradient centrifugation, the soluble BP180 demonstrated a va
lue of approximately 7 S, and chemical cross-linking experiments revea
led a trimer form, The calculated frictional ratio, f/f(0) = 2.8, sugg
ests an asymmetric configuration, For further characterization, we pur
ified the soluble BP180 by immunoaffinity column chromatography using
an anti-BP180 monoclonal antibody, Rotary shadowing images of the puri
fied BP180 showed a quaver-like molecule consisting of a globular head
, a central rod, and a flexible tail, With regard to the primary struc
ture and species comparisons, the central rod, 60-70 nm in length, pro
bably corresponds to the largest collagenous region, forming a collage
n-like triple helix, in human form, The globular head and the flexible
tail seem to correspond to the cytoplasmic and the interrupted collag
enous region, respectively, of the extracellular portions, In conclusi
on, the present demonstration of the entire configuration of BP180, wi
th a collagen-like trimer in its extracellular part, suggests that BP1
80 is one of the major components of anchoring filaments.