title: Ziploc-ing the structure: Triple helix formation is coordinated by rough endoplasmic reticulum resident PPIases.
abstract: BACKGROUND
  Protein folding is crucial for proteins' specific functions and is facilitated by various types of enzymes and molecular chaperones. The peptidyl prolyl cis/trans isomerases (PPIase) are one of these families of enzymes. They ubiquitously exist inside the cell and there are eight PPIases in the rough endoplasmic reticulum (rER), a compartment where the folding of most secreted proteins occurs.
  
  
  METHODS
  We review the functional and structural aspects of individual rER resident PPIases. Furthermore, we specifically discuss the role of these PPIases during collagen biosynthesis, since collagen is the most abundant protein in humans, is synthesized in the rER, and contains a proportionally high number of proline residues.
  
  
  CONCLUSIONS
  The rER resident PPIases recognize different sets of substrates and facilitate their folding. Although they are clearly catalysts for protein folding, they also have more broad and multifaceted functions. We propose that PPIases coordinate collagen biosynthesis in the rER.
  
  
  CONCLUSIONS
  This review expands our understanding of collagen biosynthesis by explaining the influence of novel indirect mechanisms of regulating folding and this is also explored for PPIases. We also suggest future directions of research to obtain a better understanding of collagen biosynthesis and functions of PPIases in the rER. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97239, USA; Shriners Hospital for Children, Research Department, Portland, OR 97239, USA.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ishikawa
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97239, USA; Shriners Hospital for Children, Research Department, Portland, OR 97239, USA.
authors.forename: Sergei
authors.initials: S
authors.lastname: Boudko
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97239, USA; Shriners Hospital for Children, Research Department, Portland, OR 97239, USA. Electronic address: hpb@shcc.org.
authors.forename: Hans Peter
authors.initials: HP
authors.lastname: Bächinger
mesh_terms: D000818:Animals; D003094:Collagen / Q000096:biosynthesis*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D019696:Peptidylprolyl Isomerase / Q000378:metabolism*; D017510:Protein Folding; D017433:Protein Structure, Secondary
chemical_list: D003094:Collagen; D019696:Peptidylprolyl Isomerase
keywords: Collagen; Molecular chaperone; Peptidyl prolyl cis/trans isomerase; Protein folding; Protein–protein interaction; Rough endoplasmic reticulum