Structural similarity between lung surfactant protein D and conglutinin. Two distinct, C-type lectins containing collagen-like sequences.
Preparations of bovine lung surfactant D (SP-D) and conglutinin were examined by electron microscopy, gel-filtration and SDS/PAGE. SP-D is composed of non-covalently linked subunits, of 160 kDa, which each contain three, disulphide-linked, 44-kDa polypeptide chains. In the electron microscope a single 160-kDa subunit of SP-D appears as a 45.8 +/- 3-nm-long rod connected to a small globular 'head'. Particles were also seen which correspond to non-covalently linked dimers, trimers and tetramers of the 160-kDa monomer subunit of SP-D. The tetramer structure contains 12 polypeptide chains and is very similar to the electron microscopy images and model reported by Strang et al. [Strang, C. J., Slayter, US., Lachmann, P. J. and Davis, A. E. (1986) Biochem. J. 236, 3811-389] for bovine conglutinin in which four 160-kDa subunits are disulphide-linked to give a molecule of expected molecular mass of 528 kDa. This study confirmed the findings by Strang et al. in the above paper for intact conglutinin and also emphasised that the rod-like structures, of length 37.6 +/- 3.7 nm, seen in the conglutinin subunits were significantly shorter than those in SP-D despite the close similarity in amino acid sequence (79% identify) and chain length between the two proteins. In addition, a truncated form of conglutinin was found in the conglutinin preparations, due to limited proteolysis of the Arg-Ala bond at position 54 in the 44-kDa chains. These truncated conglutinin chains yield a subunit composed of three shortened, non-disulphide-linked, chains and this subunit appears as a monomer with a rod length of 34.2 +/- 2.8 nm in the electron microscope. On gel-filtration, a proportion of the SP-D preparation behaved, as expected, as a molecule with an apparent molecular mass of 600 kDa. The remainder of the SP-D preparation behaved as aggregated material with a molecular mass greater than 900 kDa which yielded no distinct structures in the electron microscope. Intact conglutinin was eluted at a position greater than 900 kDa but yet provided clear electron microscopy images of the tetramer structure described above.(ABSTRACT TRUNCATED AT 400 WORDS)
Lu
J
J
Department of Biochemistry, University of Oxford, England.
Wiedemann
H
H
Holmskov
U
U
Thiel
S
S
Timpl
R
R
Reid
K B
KB
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D003094:Collagen / Q000737:chemistry*; D037222:Collectins; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000737:chemistry* / Q000648:ultrastructure; D006801:Humans; D037102:Lectins / Q000737:chemistry*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D011487:Protein Conformation; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000648:ultrastructure; D012712:Serum Globulins / Q000737:chemistry*
D037222:Collectins; D006023:Glycoproteins; D037102:Lectins; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants; D012712:Serum Globulins; C024014:conglutinin; D003094:Collagen