Structure of canine pulmonary surfactant apoprotein: cDNA and complete amino acid sequence.

Abstract

The apoproteins of pulmonary surfactant (PSAP) are thought to be critical for normal surfactant function. They bind to surfactant phospholipids and enhance their ability to form surface ifims in vitro. These acidic glycoproteins have monomeric molecular weights of 36,000, 32,000, and 28,000 . Each member of this family of proteins has a similar amino acid composition and their differences in electrophoretic mobility are due in part to glycosylation. We have derived the full amino acid sequence of PSAP-32 from the nucleotide sequence of PSAP cDNA. A cDNA library was prepared from canine lung poly(A)+ RNA and screened with oligonucleotide probes that were based on the NH2-terminal amino acids of PSAP-32 determined by Edman degradation. This protein has the striking feature of collagen-like and non-collagen-like sequences in the same polypeptide chain. There are 24 Gly-Xaa-Yaa triplets, where Yaa is often hydroxyproline. These repeats comprise one-third of PSAP near the NH2 terminus. The remaining two-thirds of PSAP is resistant to bacterial collagenase digestion and contains a possible N-glycosylation site near the carboxyl terminus. The NH2-terminal one-third of PSAP-32 probably contains the cysteine involved in interchain disulflde bonds.Lung surfactant is a mixture of lipids and proteins in part responsible for the maintenance of alveolar stability by lowering the surface tension at the air-liquid interface (1). To decrease the interfacial tension, lung surfactant must be able to rapidly form a surface film. Previously, King and Clements (2) demonstrated that protein-depleted canine surfactant lipids formed surface films more slowly than the intact surfactant containing about 10% protein. They showed that two proteins (Mr 34,000 and 10,000) in canine lung surfactant were lung-specific (3). While the smaller of these proteins has not been extensively investigated, acidic glycoproteins of Mr 28,000-40,000 have been identified in the lung surfactant from several species (4-11).The ability of isolated canine surfactant proteins of Mr 28,000-40,000 to enhance the rate of surface film formation in vitro has been investigated. These proteins readily associate with synthetic phospholipids (12) and extracted surfactant lipids (13,14) and in the presence of calcium ions promote extremely rapid formation of phospholipid surface films (14). Calcium ions are also required for the rapid spreading of native canine surfactant (13). These results have suggested a critical role for pulmonary surfactaInt apoprotein (PSAP) in normal lung function.Canine PSAP comprises a family of proteins of Mr 28,000, 32,000, and 36,000 (PSAP-28, -32, and -36) (15). They have the same NH2-terminal amino acid, isoleucine, and have nearly identical amino acid compositions. All three contain large quantities of glycine (17 mol %) and proline (10 mol %). Approximately half of the prolines are hydroxylated. These proteins are variably glycosylated. Removal of the carbohydrate from PSAP-32 and PSAP-36 by endoglycosidase F digestion results in p...

Collectins — soluble proteins containing collagenous regions and lectin domains — and their roles in innate immunity

“…Therefore, although the requirement for hydroxyl-groups of the mannose-or galactose-type within the binding-site on the carbohydrate molecules is determined by the E-N/Q-D pair of residues, other differences seen in the sequences of the lectin domains, and of the extensive loop carrying the binding sites in particular, seem to be also involved in ligand selection in the in vivo interaction of C-type lectins with complex carbohydrate structures. Domains identified by sequence comparison and predicted to have an overall folding similar to that seen in the crystal structure of the C-type lectin domain of MBP (Weis et al, 1991b), but lacking some of the characteristic residues involved in calcium/carbohydrate binding, are seen in a number of type I1 membrane proteins ( QPD-E-WND gal Tanaka et al, 1988 QPD-E-WND gal Zimmerman & Ruoslahti, 1989 QPD-E-WND gal Drickamer, 1981Spiess & Lodish, 1985Drickamer et al, 1984Ii et al, 1990Hoyle & Hill, 1991Sat0 et al, 1992Curtis et al, 1992Suter et al, 1987Yokoyama et al, 1989Chan & Takei, 1989Giorda et al, 1990Van Hoegen et al, 1990Houchins et al, 1991Wong et al, 1991Yoshimatsu et al, 1992Lee et al, 1991Taylor et al, 1989Drickamer et al, 1986White et al, 1985Benson et al, 1985Rust et al, 1991Holmskov et al, 1993bHolmskov et al, 1993aLasky et al, 1989Bevilacqua et al, 1991Johnson et al, 1989Christa et al, 1994Ng & Hew, 1992Ewart et al, 1992Rouquier et al, 1991Taylor et al, 1990 EPN-E-WND man (Drickamer, 1992). Not all of the carbohydrate specificities have been determined (*), and certain proteins, although a Proteins containing C-type lectin domains or regions w...…”

Effect of canine surfactant protein (SP‐A) on the respiratory burst of phagocytic cells

“…SP-A can bind lipids [4] and mannose in a lectin-like manner [5]. Amino acid sequences from human [6,7] and dog SP-A [8] revealed a collagenlike region within the NHz-terminal half and a globular region within the COOH-terminal half of the polypeptide chain. Analysis of the macromolecular organization proved that SP-A aggregates to a complex of 18 polypeptides with 6 collagen-triple helices [9,10], and that this structure is highly homologous to the hexameric structure of Clq [9], a subcomponent of the first component of the classical complement pathway.…”

Estimation and Reliability of Molecular Sequence Alignments

“…To illustrate the methods, the partial amino acid sequences of chicken hepatic lectin (Drickhamer 1981) and dog pulmonary surfactant (Benson et al 1985) that were previously examined by Zuker (1991) are compared. The maximum likelihood parameter estimates shown in Table 1 are for the generalized model (both with and without special treatment of terminal events).…”