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Biomedical subjects

D K Clawson

Publications and source records attributed to D K Clawson.

At least 19 recordsLinked to original sources
PubMed2000

Crystal structure of human parathyroid hormone 1-34 at 0.9-A resolution.

The N-terminal fragment 1-34 of parathyroid hormone (PTH), administered intermittently, results in increased bone formation in patients with osteoporosis. PTH and a related molecule, parathyroid hormone-related peptide (PTHrP), act on cells via a common PTH/PTHrP receptor. To define more precisely the ligand-receptor interactions, we have crystallized human PTH (hPTH)-(1-34) and determined the structure to 0.9-A resolution. hPTH-(1-34) crystallizes as a slightly bent, long helical dimer. Analysis reveals that the extended helical conformation of hPTH-(1-34) is the likely bioactive conformation. We have developed molecular models for the interaction of hPTH-(1-34) and hPTHrP-(1-34) with the PTH/PTHrP receptor. A receptor binding pocket for the N terminus of hPTH-(1-34) and a hydrophobic interface with the receptor for the C terminus of hPTH-(1-34) are proposed.

Amino Acid Sequence↗
PubMed2000

The crystal structures of human alpha-thrombin complexed with active site-directed diamino benzo[b]thiophene derivatives: a binding mode for a structurally novel class of inhibitors.

The crystal structures of four active site-directed thrombin inhibitors, 1-4, in a complex with human alpha-thrombin have been determined and refined at up to 2.0 A resolution using X-ray crystallography. These compounds belong to a structurally novel family of inhibitors based on a 2,3-disubstituted benzo[b]thiophene structure. Compared to traditional active-site directed inhibitors, the X-ray crystal structures of these complexes reveal a novel binding mode. Unexpectedly, the lipophilic benzo[b]thiophene nucleus of the inhibitor appears to bind in the S1 specificity pocket. At the same time, the basic amine of the C-3 side chain of the inhibitor interacts with the mostly hydrophobic proximal, S2, and distal, S3, binding sites. The second, basic amine side chain at C-2 was found to point away from the active site, occupying a location between the S1 and S1' sites. Together, the aromatic rings of the C-2 and C-3 side chains sandwich the indole ring of Trp60D contained in the thrombin S2 insertion loop defined by the sequence "Tyr-Pro-Pro-Trp." [The thrombin residue numbering used in this study is equivalent to that reported for chymotrypsinogen (Hartley BS, Shotton DM, 1971, The enzymes, vol. 3. New York: Academic Press. pp 323-373).] In contrast to the binding mode of more classical thrombin inhibitors (D-Phe-Pro-Arg-H, NAPAP, Argatroban), this novel class of benzo[b]thiophene derivatives does not engage in hydrogen bond formation with Gly216 of the thrombin active site. A detailed analysis of the three-dimensional structures not only provides a clearer understanding of the interaction of these agents with thrombin, but forms a foundation for rational structure-based drug design. The use of the data from this study has led to the design of derivatives that are up to 2,900-fold more potent than the screening hit 1.

Binding Sites↗
PubMed1999

Dibasic benzo[b]thiophene derivatives as a novel class of active site directed thrombin inhibitors: 2. Sidechain optimization and demonstration of in vivo efficacy.

Potent, subnanomolar thrombin inhibitors 4, 5, and 6 are developed through side chain optimization of novel, benzo[b]thiophene-based small organic entities 2 and 3 and through SAR additivity studies of the new structural elements identified. X-ray crystallographic studies of 4b-thrombin complex revealed a hydrophobic and an electrostatic interaction of these new elements with thrombin at the S2 and S3 binding sites. In vitro and in vivo pharmacological studies showed that 4, 5, and 6 are potent anticoagulants in human plasma with demonstrated antithrombotic efficacy in a rat model of thrombosis.

Animals↗
PubMed1999

Challenges and opportunities of racial diversity in medical education.

Racial and cultural diversity in the physician workforce (in orthopaedics this includes women) is an essential if the best healthcare for the American people is to be provided. The percentage of minorities to the white population is increasing yet their representation in medical schools and the practicing community has not risen at that same pace. Affirmative Action efforts continue to be challenged as lowering standards and depriving better qualified students admission to medical schools. Admissions committees and orthopaedic residency directors should recognize that grade point averages and test scores may not be the best predictors of how well a physician or surgeon cares for patients. How far a person has come and what obstacles they have had to overcome, their demonstrated caring and compassion for people, their understanding of diverse cultures and languages may be a far better predictor of the quality of care physicians give to their patients. Affirmative Action should not be looked on as lowering standards, but using all available information in the selection process for medical school and residency training to ensure that the medical profession more closely mirrors the diverse racial and ethnic background of the United States population. How far a person has come and the adversity they have overcome may have far greater impact on making the correct diagnosis and setting out a proper treatment plan that the patient will accept than mastering test taking in the biologic and physical sciences. Obtaining racial and cultural diversity in the medical profession should be a national imperative.

Cultural Diversity↗
PubMed1998

Dibasic benzo[b]thiophene derivatives as a novel class of active site directed thrombin inhibitors. 2. Exploring interactions at the proximal (S2) binding site.

In an effort to increase the thrombin inhibitory activity of a novel series of inhibitors (i.e., 1a), substituents were incorporated at the C-3" position of the C-3 aryl ring (2). Consistent with the X-ray crystallography studies, small hydrophobic groups at the C-3" site (Br and Me) enhanced thrombin inhibitory activity by 8-fold. However, a few more hydrophilic substituents (NO2 and OMe) also enhanced the potency of the series. The biological results are discussed in terms of molecular modeling studies.

Binding Sites↗
PubMed1997

Viracept (nelfinavir mesylate, AG1343): a potent, orally bioavailable inhibitor of HIV-1 protease.

Using a combination of iterative structure-based design and an analysis of oral pharmacokinetics and antiviral activity, AG1343 (Viracept, nelfinavir mesylate), a nonpeptidic inhibitor of HIV-1 protease, was identified. AG1343 is a potent enzyme inhibitor (Ki = 2 nM) and antiviral agent (HIV-1 ED50 = 14 nM). An X-ray cocrystal structure of the enzyme-AG1343 complex reveals how the novel thiophenyl ether and phenol-amide substituents of the inhibitor interact with the S1 and S2 subsites of HIV-1 protease, respectively. In vivo studies indicate that AG1343 is well absorbed orally in a variety of species and possesses favorable pharmacokinetic properties in humans. AG1343 (Viracept) has recently been approved for marketing for the treatment of AIDS.

Administration, Oral↗
PubMed1997

Crystal structure of the obese protein leptin-E100.

Mutations in the obese gene (OB) or in the gene encoding the OB receptor(OB-R) result in obesity, infertility and diabetes in a variety of mouse phenotypes. The demonstration that OB protein (also known as leptin) can normalize body weight in ob/ob mice has generated enormous interest. Most human obesity does not appear to result from a mutant form of leptin: rather, serum leptin concentrations are increased and there is an apparent inability to transport it to the central nervous system (CNS). Injection of leptin into the CNS of overfed rodents resistant to peripheral administration was found to induce biological activity. Consequently, for the leptin to act as a weight-lowering hormone in human obesity, it appears that appropriate concentrations must be present in the CNS. This places a premium on understanding the structure of the hormone in order to design more potent and selective agonists. Here we report the crystal structure at 2.4A resolution of a human mutant OB protein (leptin-E100) that has comparable biological activity to wild type but which crystallizes more readily. The structure reveals a four-helix bundle similar to that of the long-chain helical cytokine family.

Amino Acid Sequence↗
PubMed1997

The crystal structure of human alpha-thrombin complexed with LY178550, a nonpeptidyl, active site-directed inhibitor.

The crystal structure of human alpha-thrombin in complex with LY178550, a nonpeptidyl, active site-directed inhibitor, has been solved to 2.07 A resolution by the method of X-ray crystallography. The final model of the complex has a crystallographic R-value of 21.5% (Rfree = 23.1%) with 0.014 A and 2.4 degrees standard deviation from ideal bond lengths and angles, respectively. Well-defined electron density was observed for the inhibitor in the active site. The inhibitor binds to the active site in an L-shaped manner, mimicking the bound conformation of the tripeptide arginal series of thrombin inhibitors (Chirgadze NY et al., 1992, American Crystallographic Association Meeting 20: 116 [Abstr. PB311]). The basic amidine of LY178550 forms a salt bridge with Asp 189 within the specificity pocket, while the 4-benzylpiperidine side chain engages in a number of hydrophobic interactions at the S2 and S3 binding sites. The inhibitor does not interact in any fashion with the active site sequence Ser 214-Gly 216, as occurs with many of the inhibitors studied previously. The indole N-H of the inhibitor forms a hydrogen bond to the gamma-oxygen of the catalytic serine (Ser 195).

Binding Sites↗
PubMed1996

Indole inhibitors of human nonpancreatic secretory phospholipase A2. 1. Indole-3-acetamides.

Phospholipases (PLAs) produce rate-limiting precursors in the biosynthesis of various types of biologically active lipids involved in inflammatory processes. Increased levels of human nonpancreatic secretory phospholipase A2 (hnps-PLA2) have been detected in several pathological conditions. An inhibitor of this enzyme could have therapeutic utility. A broad screening program was carried out to identify chemical structures which could inhibit hnps-PLA2. One of the lead compounds generated by the screening program was 5-methoxy-2-methyl-1-(phenylmethyl)-1H-indole-3-acetic acid (13a). We describe the syntheses, structure--activity relationships, and pharmacological activities of a series of indole-3-acetamides and related compounds derived from this lead. This SAR was undertaken with the aid of X-ray crystal structures of complexes between the inhibitors and hnps-PLA2 which were of great value in directing the SAR.

Animals↗
PubMed1996

Indole inhibitors of human nonpancreatic secretory phospholipase A2. 2. Indole-3-acetamides with additional functionality.

As reported in our previous paper, a series of indole-3-acetamides which possessed potency and selectivity as inhibitors of human nonpancreatic secretory phospholipase A2(hnps-PLA2) was developed. The design of these compounds was based on information derived from x-ray crystal structures determined for complexes between the enzyme and its inhibitors. We describe here the further implementation of this structure-based design strategy and continued SAR development to produce indole-3-acetamides with additional functionalities which provide increased interaction with important residues within the enzyme active site. These efforts led to inhibitors with substantially enhanced potency and selectivity.

Crystallography, X-Ray↗
PubMed1996

Indole inhibitors of human nonpancreatic secretory phospholipase A2. 3. Indole-3-glyoxamides.

The preceding papers of this series detail the development of functionalized indole-3-acetamides as inhibitors of hnps-PLA2. We describe here the extension of the structure-activity relationship to include a series of indole-3-glyoxamide derivatives. Functionalized indole-3-glyoxamides with an acidic substituent appended to the 4- or 5-position of the indole ring were prepared and tested as inhibitors of hnps-PLA2. It was found that the indole-3-glyoxamides with a 4-oxyacetic acid substituent had optimal inhibitory activity. These inhibitors exhibited an improvement in potency over the best of the indole-3-acetamides, and LY315920 (6m) was selected for evaluation clinically as an hnps-PLA2 inhibitor.

Crystallography, X-Ray↗
PubMed1995

Structure-based design of the first potent and selective inhibitor of human non-pancreatic secretory phospholipase A2.

A lead compound obtained from a high volume human non-pancreatic secretory phospholipase A2 (hnps-PLA2) screen has been developed into a potent inhibitor using detailed structural knowledge of inhibitor binding to the enzyme active site. Four crystal structures of hnps-PLA2 complexed with a series of increasingly potent indole inhibitors were determined and used as the structural basis for both understanding this binding and providing valuable insights for further development. The application of structure-based drug design has made possible improvements in the binding of this screening lead to the enzyme by nearly three orders of magnitude. Furthermore, the optimized structure (LY311727) displayed 1,500-fold selectivity when assayed against porcine pancreatic s-PLA2.

Animals↗
PubMed1991

Structure of recombinant human rheumatoid arthritic synovial fluid phospholipase A2 at 2.2 A resolution.

Phospholipases A2 (PLA2s) may be grouped into distinct families of proteins that catalyse the hydrolysis of the 2-acyl bond of phospholipids and perform a variety of biological functions. The best characterized are the small (relative molecular mass approximately 14,000) calcium-dependent, secretory enzymes of diverse origin, such as pancreatic and venom PLA2s. The structures and functions of several PLA2s are known. Recently, high-resolution crystal structures of complexes of secretory PLA2s with phosphonate phospholipid analogues have provided information about the detailed stereochemistry of transition-state binding, confirming the proposed catalytic mechanism of esterolysis. By contrast, studies on mammalian nonpancreatic secretory PLA2s (s-PLA2s) have only recently begun; s-PLA2s are scarce in normal cells and tissues but large amounts are found in association with local and systemic inflammatory processes and tissue injury in animals and man. Such s-PLAs have been purified from rabbit and rat inflammatory exudate, from synovial fluid from patients with rheumatoid arthritis and from human platelets. Cloning and sequencing shows that the primary structure of the human s-PLA2 has about 37% homology with that of bovine pancreatic PLA2 and 44% homology with that of Crotalus atrox PLA2. The human s-PLA2 is an unusually basic protein, yet contains most of the highly conserved amino-acid residues and sequences characteristic of the PLA2s sequenced so far. Here we report the refined, three-dimensional crystal structure at 2.2 A resolution of recombinant human rheumatoid arthritic synovial fluid PLA2. This may aid the development of potent and specific inhibitors of this enzyme using structure-based design.

Arthritis, Rheumatoid↗
PubMed1990

The education of the physician.

Although the quality of U.S. medical care is at an all-time high, thanks largely to the education and training of American physicians, the nation is in a health care crisis, especially in rural areas and the inner cities. To meet this challenge, change in the education of physicians is required. An important reason for the present crisis is that the selection and education process has encouraged only science- and high-technology-oriented individuals to enter medicine, even though social and behavioral factors are the basis of a majority of today's medical problems. The author realizes that there is little motivation for frequently overburdened faculties and underfunded medical schools to undertake the needed changes; he describes various problems that challenge the existence of the health care system, including the increasing (and well-meaning) involvement in educational matters by legislators and bureaucrats. The author then explores various options for bringing about reform of physician education, including changes in premedical education, in the criteria used for identifying and admitting promising students, and in various aspects of medical education. Such reform could encourage some of the best, brightest, and more broadly educated students to enter the medical profession and could maintain high standards of physician education while fulfilling a public trust and meeting a public need.

Education, Medical, Undergraduate↗