Search PubMed⌕ Search

Biomedical subjects

M A Fleming

Publications and source records attributed to M A Fleming.

8 recordsLinked to original sources
PubMed1995

X-ray structure of calcineurin inhibited by the immunophilin-immunosuppressant FKBP12-FK506 complex.

The X-ray structure of the ternary complex of a calcineurin A fragment, calcineurin B, FKBP12, and the immunosuppressant drug FK506 (also known as tacrolimus) has been determined at 2.5 A resolution, providing a description of how FK506 functions at the atomic level. In the structure, the FKBP12-FK506 binary complex does not contact the phosphatase active site on calcineurin A that is more than 10 A removed. Instead, FKBP12-FK506 is so positioned that it can inhibit the dephosphorylation of its macromolecular substrates by physically hindering their approach to the active site. The ternary complex described here represents the three-dimensional structure of a Ser/Thr protein phosphatase and provides a structural basis for understanding calcineurin inhibition by FKBP12-FK506.

Amino Acid Sequence↗
PubMed1994

Enthalpy of hydrogen bond formation in a protein-ligand binding reaction.

Parallel measurements of the thermodynamics (free-energy, enthalpy, entropy and heat-capacity changes) of ligand binding to FK506 binding protein (FKBP-12) in H2O and D2O have been performed in an effort to probe the energetic contributions of single protein-ligand hydrogen bonds formed in the binding reactions. Changing tyrosine-82 to phenylalanine in FKBP-12 abolishes protein-ligand hydrogen bond interactions in the FKBP-12 complexes with tacrolimus or rapamycin and leads to a large apparent enthalpic stabilization of binding in both H2O and D2O. High-resolution crystallographic analysis reveals that two water molecules bound to the tyrosine-82 hydroxyl group in unliganded FKBP-12 are displaced upon formation of the protein-ligand complexes. A thermodynamic analysis is presented that suggests that the removal of polar atoms from water contributes a highly unfavorable enthalpy change to the formation of C=O...HO hydrogen bonds as they occur in the processes of protein folding and ligand binding. Despite the less favorable enthalpy change, the entropic advantage of displacing two water molecules upon binding leads to a slightly more favorable free-energy change of binding in the reactions with wild-type FKBP-12.

Carrier Proteins↗
PubMed1992

Expression and characterization of human FKBP52, an immunophilin that associates with the 90-kDa heat shock protein and is a component of steroid receptor complexes.

Using an FK506 affinity column to identify mammalian immunosuppressant-binding proteins, we identified an immunophilin with an apparent M(r) approximately 55,000, which we have named FKBP52. We used chemically determined peptide sequence and a computerized algorithm to search GenPept, the translated GenBank data base, and identified two cDNAs likely to encode the murine FKBP52 homolog. We amplified a murine cDNA fragment, used it to select a human FKBP52 (hFKBP52) cDNA clone, and then used the clone to deduce the hFKBP52 sequence (calculated M(r) 51,810) and to express hFKBP52 in Escherichia coli. Recombinant hFKBP52 has peptidyl-prolyl cis-trans isomerase activity that is inhibited by FK506 and rapamycin and an FKBP12-like consensus sequence that probably defines the immunosuppressant-binding site. FKBP52 is apparently common to several vertebrate species and associates with the 90-kDa heat shock protein (hsp90) in untransformed mammalian steroid receptor complexes. The putative immunosuppressant-binding site is probably distinct from the hsp90-binding site, and we predict that FKBP52 has different structural domains to accommodate these functions. hFKBP52 contains 12 protein kinase phosphorylation-site motifs and a potential calmodulin-binding site, implying that posttranslational phosphorylation could generate multiple isoforms of the protein and that calmodulin and intracellular Ca2+ levels could affect FKBP52 function. FKBP52 transcripts are present in a variety of human tissues and could vary in abundance and/or stability.

Amino Acid Isomerases↗
PubMed1992

Saccharomyces cerevisiae contains a homolog of human FKBP-13, a membrane-associated FK506/rapamycin binding protein.

FKB2 encodes a homolog of human FKBP-13, a membrane-associated binding protein for the immunosuppressants FK506 and rapamycin. FKB2 is located on the right arm of chromosome IV and contains an open reading frame of 135 amino acids, of which the first 17 residues comprise a putative hydrophobic leader peptide. Yeast FKBP-13 is homologous to human FKBP-13 (52% amino acid identity) and to FKBP-12, the major cytosolic receptor for FK506. In the alignment of FKBP-13 and FKBP-12 sequences, there are 28 invariant residues. Among these conserved residues are those that comprise the drug binding and peptidyl-prolyl cis-trans isomerase active site of FKBP-12. The phylogenetic conservation of the FKBP family suggest that the proteins are involved in a basic cellular function.

Amino Acid Sequence↗
PubMed1973

Knee arthrography.

Explore the source record for details and available documents.

Cartilage, Articular↗