Human pulmonary-surfactant-associated protein C (SP-C) is an extremely hydrophobic peptide comprising 34-35 amino acids. It is involved in the reduction of surface tension at the air/liquid in the lung. In order to understand the mechanism by which this molecule is generated from its 197-amino-acid-residues-long precursor and secreted into the alveolar space, we analysed the biosynthesis and processing of this precursor in an ‘in vitro’ system. Our results show that the SP-C precursor is a 21 kDa integral membrane protein. It is anchored in the membrane by a hydrophobic domain that comprises the 20-amino-acid-residues-long hydrophobic core of the mature SP-C peptide. The N-terminus remains in the cytoplasm, which leads to a type II transmembrane orientation of the precursor. Membrane integration occurs in a signal-peptidase-independent manner. The hydrophobic domain acts as both signal sequence and membrane-anchoring domain. We suggest that correct membrane insertion of the SP-C precursor, which is strictly dependent on the hydrophobic-amino-acid sequence represented by the hydrophobic core of the mature SP-C, is itself a prerequisite for further processing and intracellular transport of the mature SP-C.
Research Article|July 15 1991
The pulmonary surfactant protein C (SP-C) precursor is a type II transmembrane protein
H R Eistetter;
Biochem J (1991) 277 (2): 493-499.
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A Keller, H R Eistetter, T Voss, K P Schäfer; The pulmonary surfactant protein C (SP-C) precursor is a type II transmembrane protein. Biochem J 15 July 1991; 277 (2): 493–499. doi: https://doi.org/10.1042/bj2770493
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