Protein disulphide isomerase, a multifunctional endoplasmic reticulum protein

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Protein disulphide isomerase (PDI) is a key enzyme involved in protein folding and modification within the endoplasmic reticulum.
• PDI plays critical roles in disulfide bond formation, isomerization, and reduction, essential for the proper function of many secreted proteins.

Purpose of the Study:

• To characterize the structure, function, and genetic organization of Protein disulphide isomerase (PDI) and its isoforms.
• To investigate the cellular localization and functional diversity of PDI within vertebrate tissues.

Main Methods:

• Purification, cloning, and sequencing of PDI from various vertebrate tissues.
• Analysis of PDI sequence similarity across different species (human and chick).
• Chromosomal localization of human PDI genes using cDNA probes.

Main Results:

• PDI exhibits multiple functions including procollagen hydroxylation, disulfide bond catalysis, thyroid hormone binding, and oligosaccharide transferase activity.
• PDI concentration correlates with endoplasmic reticulum activity in secreting disulfide-bonded polypeptides.
• Human PDI isoforms show high sequence similarity (97%), while chick isoforms exhibit lower similarity (80%).
• Human PDI genes are localized to opposite ends of chromosome 17's long arm.

Conclusions:

• PDI exists as a family of related polypeptides localized to the endoplasmic reticulum lumen.
• The N-terminal signal peptide directs PDI into the ER, and a C-terminal KDEL sequence retains it within the ER.
• The distinct chromosomal localization of human PDI genes suggests a complex evolutionary history and potential for differential regulation.