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Role of cysteine residues in human plasma phospholipid transfer protein

S J Qu1, H Z Fan, C Kilinc

  • 1Department of Medicine, Baylor College of Medicine, and The Methodist Hospital, Houston, Texas 77030, USA.

Journal of Protein Chemistry
|May 20, 1999
PubMed

Insights

Mutations in specific cysteine residues of phospholipid transfer protein (PLTP) impact its secretion and activity. Cys129 and Cys168 are crucial for PLTP secretion, while Cys5 and Cys318 affect synthesis and secretion but not activity.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Protein Science

Background:

  • Phospholipid transfer protein (PLTP) is a human plasma lipid transfer protein involved in lipid metabolism.
  • PLTP shares a gene family with bactericidal/permeability-increasing protein, featuring conserved cysteine residues.
  • The role of specific cysteine residues in PLTP secretion and function was previously unclear.

Purpose of the Study:

  • To investigate the importance of conserved cysteine residues (Cys129, Cys168) and other cysteines (Cys5, Cys318) in PLTP secretion and activity.
  • To elucidate the functional significance of disulfide bonds involving these cysteine residues.

Main Methods:

  • Site-directed mutagenesis was used to replace cysteine residues with glycine.
  • Wild-type and mutant PLTP cDNAs were expressed in COS-6 cells.
  • PLTP secretion, mass, and activity were analyzed in cell lysates and culture medium.

Main Results:

  • Mutations at Cys129 and Cys168 rendered PLTP secretion incompetent, with no detectable mass or activity.
  • Mutations at Cys5 and Cys318 resulted in partially impaired PLTP synthesis and secretion.
  • Specific activities of Cys5 and Cys318 mutants were comparable to wild-type PLTP, indicating glycosylation does not affect transfer activity.

Conclusions:

  • Cys129 and Cys168 are essential for PLTP secretion, likely through disulfide bond formation.
  • Cys5 and Cys318 play roles in PLTP synthesis and secretion but are not critical for its lipid transfer activity.
  • These findings enhance understanding of PLTP structure-function relationships and lipid transport mechanisms.

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