The pulmonary surfactant protein C (SP-C) precursor is a type II transmembrane protein

Biochem J. 1991 Jul 15;277 ( Pt 2)(Pt 2):493-9. doi: 10.1042/bj2770493.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Chloramphenicol O-Acetyltransferase / genetics
  • Chloramphenicol O-Acetyltransferase / metabolism
  • DNA / genetics
  • Endopeptidases / metabolism
  • Humans
  • Membrane Proteins / genetics*
  • Microsomes / metabolism
  • Molecular Sequence Data
  • Molecular Weight
  • Plasmids
  • Protein Biosynthesis
  • Protein Precursors / genetics*
  • Protein Processing, Post-Translational
  • Proteolipids / genetics*
  • Proteolipids / isolation & purification
  • Pulmonary Surfactants / genetics*
  • Pulmonary Surfactants / isolation & purification
  • RNA, Messenger / genetics
  • Rabbits
  • Restriction Mapping
  • Reticulocytes / metabolism
  • Transcription, Genetic

Substances

  • Membrane Proteins
  • Protein Precursors
  • Proteolipids
  • Pulmonary Surfactants
  • RNA, Messenger
  • DNA
  • Chloramphenicol O-Acetyltransferase
  • Endopeptidases