Oren Bogin

Insight into Schmid Metaphyseal Chondrodysplasia from the Crystal Structure of the Collagen X NC1 Domain Trimer

Collagen X is expressed specifically in the growth plate of long bones. Its C1q-like C-terminal NC1 domain forms a stable homotrimer and is crucial for collagen X assembly. Mutations in the NC1 domain cause Schmid metaphyseal chondrodysplasia (SMCD). The crystal structure at 2.0 A resolution of the human collagen X NC1 domain reveals an intimate trimeric assembly strengthened by a buried cluster of calcium ions. Three strips of exposed aromatic residues on the surface of NC1 trimer are likely to be involved in the supramolecular assembly of collagen X. Most internal SMCD mutations probably prevent protein folding, whereas mutations of surface residues may affect the collagen X suprastructure in a dominant-negative manner.

Structural basis for the enhanced thermal stability of alcohol dehydrogenase mutants from the mesophilic bacterium Clostridium beijerinckii: contribution of salt bridging

Previous research in our laboratory comparing the three‐dimensional structural elements of two highly homologous alcohol dehydrogenases, one from the mesophile Clostridium beijerinckii (CbADH) and the other from the extreme thermophile Thermoanaerobacter brockii (TbADH), suggested that in the thermophilic enzyme, an extra intrasubunit ion pair (Glu224‐Lys254) and a short ion‐pair network (Lys257‐Asp237‐Arg304‐Glu165) at the intersubunit interface might contribute to the extreme thermal stability of TbADH. In the present study, we used site‐directed mutagenesis to replace these structurally strategic residues in CbADH with the corresponding amino acids from TbADH, and we determined the effect of such replacements on the thermal stability of CbADH. Mutations in the intrasubunit ion pair region increased thermostability in the single mutant S254K‐ and in the double mutant V224E/S254K‐CbADH, but not in the single mutant V224E‐CbADH. Both single amino acid replacements, M304R‐ and Q165E‐CbADH, in the region of the intersubunit ion pair network augmented thermal stability, with an additive effect in the double mutant M304R/Q165E‐CbADH. To investigate the precise mechanism by which such mutations alter the molecular structure of CbADH to achieve enhanced thermostability, we constructed a quadruple mutant V224E/S254K/Q165E/M304R‐CbADH and solved its three‐dimensional structure. The overall results indicate that the amino acid substitutions in CbADH mutants with enhanced thermal stability reinforce the quaternary structure of the enzyme by formation of an extended network of intersubunit ion pairs and salt bridges, mediated by water molecules, and by forming a new intrasubunit salt bridge.

Crystal structure of the collagen α1(VIII) NC1 trimer

Abstract Collagen VIII is a major component of Descemets membrane and is also found in vascular subendothelial matrices. The C-terminal non-collagenous domain (NC1) domain of collagen VIII, which is a member of the C1q-like protein family, forms a stable trimer and is thought to direct the assembly of the collagen triple helix, as well as polygonal supramolecular structures. We have solved the crystal structure of the mouse α1(VIII) 3 NC1 domain trimer at 1.9 A resolution. Each subunit of the intimate NC1 trimer consists of a ten-stranded β-sandwich. The surface of the collagen VIII NC1 trimer presents three strips of partially exposed aromatic residues shown to interact with the non-ionic detergent CHAPS, which are likely to be involved in supramolecular assemblies. Equivalent strips exist in the NC1 domain of the closely related collagen X, suggesting a conserved assembly mechanism. Surprisingly, the collagen VIII NC1 trimer lacks the buried calcium cluster of the collagen X NC1 trimer. The mouse α1(VIII) and α2(VIII) NC1 domains are 71.5% identical in sequence, with the differences being concentrated on the NC1 trimer surface. A few non-conservative substitutions map to the subunit interfaces near the surface, but it is not obvious from the structure to what extent they determine the preferred assembly of collagen VIII α1 and α2 chains into homotrimers.

Crystalline alcohol dehydrogenases from the mesophilic bacterium Clostridium beijerinckii and the thermophilic bacterium Thermoanaerobium brockii: preparation, characterization and molecular symmetry.

Two tetrameric NADP(+)-dependent bacterial secondary alcohol dehydrogenases have been crystallized in the apo- and the holo-enzyme forms. Crystals of the holo-enzyme from the mesophilic Clostridium beijerinckii (NCBAD) belong to space group P2(1)2(1)2(1) with unit-cell dimensions a = 90.5, b = 127.9, c = 151.4 A. Crystals of the apo-enzyme (CBAD) belong to the same space group with unit-cell dimensions a = 80.4, b = 102.3, c = 193.5 A. Crystals of the holo-enzyme from the thermophilic Thermoanaerobium brockii (NTBAD) belong to space group P6(1(5)) (a = b = 80.6, c = 400.7 A). Crystals of the apo-form of TBAD (point mutant GI98D) belong to space group P2(1) with cell dimensions a = 123.0, b = 84.8, c = 160.4 A beta = 99.5 degrees. Crystals of CBAD, NCBAD and NTBAD contain one tetramer per asymmetric unit. They diffract to 2.0 A resolution at liquid nitrogen temperature. Crystals of TBAD(GI98D) have two tetramers per asymmetric unit and diffract to 2.7 A at 276 K. Self-rotation analysis shows that both enzymes are tetramers of 222 symmetry.

Probing structural elements of thermal stability in bacterial oligomeric alcohol dehydrogenases. I. Construction and characterization of chimeras consisting of secondary ADHs fromThermoanaerobacter brockii andClostridium beijerinckii

Two tetrameric secondary alcohol dehydrogenases (ADHs), one from the mesophileClostridium beijerinckii (CBADH) and the other from the extreme thermophileThermoanaerobacter brockii (TBADH), share 75% sequence identity but differ by 26°C in thermal stability. To explore the role of linear segments of these similar enzymes in maintaining the thermal stability of the thermostable TBADH, a series of 12 CBadh and TBadh chimeric genes and the two parental wild-type genes were expressed inEscherichia coli, and the enzymes were isolated, purified and characterized. The thermal stability of each chimeric enzyme was approximately exponentially proportional to the content of the amino acid sequence of the thermophilic enzyme, indicating that the amino acid residues contributing to the thermal stability of TBADH are distributed along the whole protein molecule. It is suggested that major structural elements of thermal stability may reside among the nine discrepant amino acid residues between the N-terminal 50-amino acid residues of TBADH and CBADH.