title: Molecular dynamics simulations reveal structural instability of human trypsin inhibitor upon D50E and Y54H mutations.
abstract: Serine protease inhibitor Kazal type 1 (SPINK1) plays an important role in protecting the pancreas against premature trypsinogen activation that causes pancreatitis. Various mutations in the SPINK1 gene were shown to be associated with patients with pancreatitis. Recent transfection studies identified intracellular folding defects, probably caused by mutation induced misfolding of D50E and Y54H mutations, as a common mechanism that reduces SPINK1 secretion and as a possible novel mechanism of SPINK1 deficiency associated with chronic pancreatitis. Using molecular dynamics, we investigated the effects of D50E and Y54H mutations on SPINK1 dynamics and conformation at 300 K. We found that the structures of D50E and Y54H mutants were less stable than and were distorted from those of the wild type, as indicated by the RMSD plots, RMSF plots and DSSP series. Specifically, unwinding of the top of helices (the main secondary structures) and the distortion of the loops above the helices were observed. It may be possible that this distorted protein structure may be recognized as "non-native" by members of the chaperone family; it may be further retained and targeted for degradation, leading to SPINK1 secretion reduction and subsequently pancreatitis in patients as Király et al. (Gut 56:1433, 2007) proposed.
authors.affiliation: National Center for Genetic Engineering and Biotechnology, 113 Thailand Science Park, Phahonyothin Road, Khlong Nueng, Khlong Luang, Pathum Thani, 12120, Thailand.
authors.forename: Wanwimon
authors.initials: W
authors.lastname: Mokmak
authors.forename: Surasak
authors.initials: S
authors.lastname: Chunsrivirot
authors.forename: Anunchai
authors.initials: A
authors.lastname: Assawamakin
authors.forename: Kiattawee
authors.initials: K
authors.lastname: Choowongkomon
authors.forename: Sissades
authors.initials: S
authors.lastname: Tongsima
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D009154:Mutation; D050500:Pancreatitis, Chronic / Q000378:metabolism; D017510:Protein Folding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D055672:Static Electricity; D013329:Structure-Activity Relationship; D014359:Trypsin Inhibitor, Kazal Pancreatic
chemical_list: D002352:Carrier Proteins; C486642:SPINK1 protein, human; D014359:Trypsin Inhibitor, Kazal Pancreatic