Jongsoo Lim

Phase equilibria of CFC alternative refrigerant mixtures : 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea) + difluoromethane (HFC-32), + 1,1,1,2-tetrafluoroethane (HFC-134a), and + 1, 1-difluoroethane (HFC-152a)

Isothermal vapor–liquid equilibria were measured for the binary systems difluoromethane (HFC-32)+1,1,1,2,3,3,3-heptafluoropropane (HFC-22ea) and 1,1-difluoroethane (HFC-152a)+1,1,1,2,3,3,3-heptafluoropropane at 283.15 and 303.15 K and 1,1,1,2-tetrafluoroethane (HFC-134a)+1,1,1,2,3,3,3-heptafluoropropane at 303.15 and 323.15 K in an apparatus in which both phases were recirculated. The experimental data were correlated with the Peng–Robinson equation of state using the Wong–Sandler mixing rules. Azeotropic behavior has not been found in any of the three mixtures.

Vapor–Liquid Equilibria of CFC Alternative Refrigerant Mixtures: Trifluoromethane (HFC-23)+Difluoromethane (HFC-32), Trifluoromethane (HFC-23)+Pentafluoroethane (HFC-125), and Pentafluoroethane (HFC-125)+1,1-Difluoroethane (HFC-152a)

Isothermal vapor–liquid equilibria for three binary mixtures of CFC alternative refrigerants were determined in an equilibrium apparatus in which both phases were continuously recirculated. The pressures and vapor and liquid compositions were measured for the binary systems trifluoromethane (HFC-23)+difluoromethane (HFC-32) and trifluoromethane (HFC-23)+pentafluoroethane (HFC-125) at 283.15 and 293.15 K and pentafluoroethane (HFC-125)+1,1-difluoroethane (HFC-152a) at 293.15 K. The experimental data were correlated with the Peng–Robinson–Stryjek–Vera equation of state using the Huron–Vidal original mixing rule. Calculated results with this equation showed good agreement with the experimental data.

Solution structure of UIM and interaction of tandem ubiquitin binding domains in STAM1 with ubiquitin

STAM1 and Hrs are the components of ESCRT-0 complex for lysosomal degradation of membrane proteins is composed of STAM1 Hrs and has multiple ubiquitin binding domains. Here, the solution structure of STAM1 UIM, one of the ubiquitin binding motif, was determined by NMR spectroscopy. The structure of UIM adopts an α-helix with amphipathic nature. The central hydrophobic residues in UIM provides the binding surface for ubiquitin binding and are flanked with positively and negatively charged residues on both sides. The docking model of STAM1 UIM-ubiquitin complex is suggested. In NMR and ITC experiments with the specifically designed mutant proteins, we investigated the ubiquitin interaction of tandem ubiquitin binding domains from STAM1. The ubiquitin binding affinity of the VHS domain and UIM in STAM1 was 52.4 and 94.9 μM, and 1.5 and 2.2 fold increased, respectively, than the value obtained from the isolated domain or peptide. The binding affinities here would be more physiologically relevant and provide more precise understanding in ESCRT pathway of lysosomal degradation.

Backbone 1H, 13C, and 15N assignments for the tandem ubiquitin binding domains of signal transducing adapter molecule 1

Signal transducing adapter molecule (STAM) forms the endosomal sorting complex required for transport-0 (ESCRT-0) complex with hepatocyte growth factor-regulated substrate (Hrs) to sort the ubiquitinated cargo proteins from the early endosomes to the ESCRT-1 complex. ESCRT-0 complex, STAM and Hrs, contains multiple ubiquitin binding domains, in which STAM has two ubiquitin binding domains, Vps27/Hrs/Stam (VHS) and ubiquitin interacting motif (UIM) at its N-terminus. By the cooperation of the multiple ubiquitin binding domains, the ESCRT-0 complex recognizes poly-ubiquitin, especially Lys63-linked ubiquitin. Here, we report the backbone resonance assignments and the secondary structure of the N-terminal 191 amino acids of the human STAM1 which includes the VHS domain and UIM. The {1H}-15N heteronuclear NOE experiments revealed that an unstructured and flexible loop region connects the VHS domain and UIM. Our work provides the basic information for the further NMR investigation of the interaction between STAM1 and poly-ubiquitin.

NMR methods in fragment based drug discovery

Nuclear magnetic resonance (NMR) spectroscopy, owing to its ability to provide atomic level information on molecular structure, dynamics and interaction, has become one of the most powerful methods in early drug discovery where hit finding and hit-to-lead generation are mainly pursued. In recent years, drug discovery programs originating from the fragment-based drug discovery (FBDD) strategies have been widely incorporated into academia and industry in which a wide variety of NMR methods become an indispensable arsenal to elucidate the binding of small molecules onto bimolecular targets. In this review, I briefly describe FBDD and introduce NMR methods mainly used in FBDD campaigns of my company. In addition, quality control of fragment library and practical NMR methods in industrial aspect are discussed shortly.

3D Structure of STAM1 UIM-ubiquitin Complex Using RosettaDock

3D structures of STAM1 UIM-ubiquitin complex were presented to predict and analyze the interaction between UIM and ubiquitin. To generate the protein-peptide complex structure, the RosettaDock method was used with and without NMR restraints. High resolution complex structure was acquired successfully and evaluated electrostatic interaction in the protein-peptide binding with several charged residues at the binding site. From docking results, the Rosettadock method could be useful to acquire essential information of protein-protein or protein-peptide interaction with minimal biological evidences.

Backbone 1 H, 15 N, and 13 C Resonance Assignment and Secondary Structure Prediction of HP1298 from Helicobacter pylori

HP1298 (Swiss-Prot ID ; P65108) is an 72-residue protein from Helicobacter pylori strain 26695. The function of HP1298 was identified as Translation initiation factor IF-l based on sequence homology, and HP1298 is included in IF-l family. Here, we report the sequence-specific backbone resonance assignments of HP1298. About 97% of all the , , , , and resonances could be assigned unambiguously. We could predict the secondary structure of HP1298, by analyzing the deviation of the and shemical shifts from their respective random coil values. Secondary structure prediction shows that HP1298 consists of six -strands. This study is a prerequisite for determining the solution structure of HP1298 and investigating the structure-function relationship of HP1298. Assigned chemical shift can be used for the study on interaction between HP1298 and other Helicobacter pylori proteins.