A A A
Dr. David Johnson

David Johnson, Ph.D.

Professor and Deputy Chairman


Room A105 Stanton Gerber Hall (Bldg. 178), VA Medical Center
Phone (423) 439-2027
Fax (423) 439-2030 
E-mail davidj@etsu.edu
Education
  • 1967 B.S. in Chemistry, University of Memphis
  • 1973 Ph.D. in Chemistry, University of Memphis  

Interdisciplinary Association

Adjunct Professor of Biological Sciences, College of Arts and Sciences, ETSU

Research Projects

Previous Studies:
Proteolytic enzymes and their inhibitors; purification, characterization, sequencing, structure function relationships, kinetics, and regulation.  Particular emphasis is placed on the roles of proteases and inhibitors in the pathogenesis of human diseases.  Work includes the discovery of the inhibitory site structure of human alpha-1-proteinase inhibitor, a genetic deficiency of which is associated with the development of pulmonary emphysema.  The oxidation of a critical methionine residue in the inhibitory site of  A-1-PI was shown to cause the loss of elastase inhibitory activity, resulting in the hypothesis that oxidants may lead to a lung-localized deficiency of functional  A-1-PI.  With this loss neutrophil elastase would  be free to degrade lung elastin, a hallmark of emphysema.  This work has led to studies of the reactions of ozone and nitrogen dioxide on the function of human  A-1-PI and the secretory leukocyte proteinase inhibitor found in human bronchial mucus.

Current Studies:
Current Studies: Presently we are focusing on human mast cell proteases, including tryptase, chymase and Cathepsin G. These serine proteases are abundant proteins stored in mast cell granules, and released upon degranulation. Tryptase is unique among the small trypsin-like proteases (31kDa) in that it forms tetramers and binds heparin. Chymase and Cathepsin G have chymotrypsin-like specificity. Studies are examining the abilities of these proteases to activate matrix metalloproteinases found in macrophage and atherosclerotic foam cells. Recombinant mast cell proteases are being expressed in the yeast Pichia pastoris, to provide sufficient quantities of these enzymes for biochemical studies.

Selected References

1: Johnson DA. Related Articles
Abstract Human mast cell proteases: activity assays using thiobenzyl ester substrates.
Methods Mol Biol. 2006;315:193-202.
PMID: 16110159 [PubMed - indexed for MEDLINE]
2: Burrows DL, Nicolaides A, Rice PJ, Dufforc M, Johnson DA, Ferslew KE. Related Articles
Abstract Papain: a novel urine adulterant.
J Anal Toxicol. 2005 Jul-Aug;29(5):275-395.
PMID: 16105251 [PubMed - in process]
3: Lockhart BE, Vencill JR, Felix CM, Johnson DA. Related Articles
Abstract Recombinant human mast-cell chymase: an improved procedure for expression in Pichia pastoris and purification of the highly active enzyme.
Biotechnol Appl Biochem. 2005 Feb;41(Pt 1):89-95.
PMID: 15163313 [PubMed - indexed for MEDLINE]
4: Kilic F, Johnson DA, Sinensky M. Related Articles
Abstract Subcellular localization and partial purification of prelamin A endoprotease: an enzyme which catalyzes the conversion of farnesylated prelamin A to mature lamin A.
FEBS Lett. 1999 Apr 30;450(1-2):61-5.
PMID: 10350058 [PubMed - indexed for MEDLINE]
5: Thomas VA, Wheeless CJ, Stack MS, Johnson DA. Related Articles
Abstract Human mast cell tryptase fibrinogenolysis: kinetics, anticoagulation mechanism, and cell adhesion disruption.
Biochemistry. 1998 Feb 24;37(8):2291-8.
PMID: 9485375 [PubMed - indexed for MEDLINE]
6: Addington AK, Johnson DA. Related Articles
Abstract Inactivation of human lung tryptase: evidence for a re-activatable tetrameric intermediate and active monomers.
Biochemistry. 1996 Oct 22;35(42):13511-8.
PMID: 8885830 [PubMed - indexed for MEDLINE]
7: Little SS, Johnson DA. Related Articles
Free in PMC Human mast cell tryptase isoforms: separation and examination of substrate-specificity differences.
Biochem J. 1995 Apr 15;307 ( Pt 2):341-6.
PMID: 7733867 [PubMed - indexed for MEDLINE]
8: Chu W, Johnson DA, Musich PR. Related Articles
Molecular cloning and characterization of mouse mast cell chymases.
Biochim Biophys Acta. 1992 May 22;1121(1-2):83-7.
PMID: 1376147 [PubMed - indexed for MEDLINE]
9: Johnson DA, Winters RS, Lee KR, Smith CE. Related Articles
Abstract Oxidant effects on rat and human lung proteinase inhibitors.
Res Rep Health Eff Inst. 1990 Dec;(37):1-39.
PMID: 1706189 [PubMed - indexed for MEDLINE]
10: Smith CE, Musich PR, Johnson DA. Related Articles
Abstract Sodium dodecyl sulfate enhancement of quantitative immunoenzyme dot-blot assays on nitrocellulose.
Anal Biochem. 1989 Feb 15;177(1):212-9.
PMID: 2662818 [PubMed - indexed for MEDLINE]
11: Johnson DA. Related Articles
Abstract Effects of ozone and nitrogen dioxide on human lung proteinase inhibitors.
Res Rep Health Eff Inst. 1987;(11):5-25.
PMID: 3268287 [PubMed - indexed for MEDLINE]

Book Chapters

Honors:
  • 1991 Wellcome visiting professor in the Laboratory of Molecular Biophysics, University of Oxford, England, May and June, "Molecular Modeling of Mast Cell Tryptases", supported by a Wellcome Foundation Travel Grant.
  • 1989 Visiting Professor, University of British Columbia, Vancouver,Canada.
  • 1987 East Tennessee State University Foundation Research Award for study of "The Biochemical Aspects of Pulmonary Diseases in Man".  This is the highest recognition given for research at ETSU each year.  Selection is made by a committee of peers.
  • 1985 Wellcome visiting scientist at Strangeways Research Laboratory, Cambridge, England, April 15 through July 15; "Human Mast Cell Tryptase".