Homocysteine in Protein Structure/Function and Human Disease

Homocysteine (Hcy) excess of is harmful to humans and is associated with increased risk of cardiovascular and neurodegenerative diseases. We found that Hcy is metabolized to the chemically reactive thioester Hcy-thiolactone as a result of an error-editing reaction in protein synthesis catalyzed by methionyl-tRNA synthetase. We also found that Hcy-thiolactone readily modifies protein lysine amino groups to form stable isopeptide bonds (N-Hcy-protein). This modification reaction alters protein structure and function, causes protein damage, and leads to pathological consequences such as an autoimmune response, thrombosis, and elastic tissue defects.

We are interested in elucidating mechanisms underlying Hcy role in human disease. We are exploring a hypothesis that N-Hcy-proteins contribute to human pathology. We found that N-Hcy-proteins are greatly elevated in genetic or nutritional disorders in Hcy (CBS deficiency) or folate metabolism (MTHFR or PCFT deficiency), that modification with Hcy-thiolactone affects protein structure and physiological activity, and that an autoimmune response to N-Hcy-protein is associated with stroke and coronary artery disease. We also found that proteolytic turnover of N-Hcy-protein in humans and mice yields N-Hcy-Lys isopeptide. We discovered protective mechanisms against Hcy-thiolactone toxicity in humans: hydrolysis by extracellular PON1/Hcy-thiolactonase carried on high-density lipoproteins (HDL, good cholesterol) in the blood and by intracellular bleomycin hydrolase/Hcy-thiolactone in tissues, and urinary elimination by the kidney.

Current research: 1. Identification of proteins targets for the modification by Hcy-thiolactone and determination of site-specific N-homocysteinylation in vivo in humans. 2. The pro-thrombotic role of N-Hcy-fibrinogen in CBS-deficient patients and mice. 4. The role of an autoimmune response against N-Hcy-protein in thrombosis. 5. Modulation of an autoimmune response and thrombosis by PON1/Hcy-thiolactonase in CBS-deficient patients. 6. The role of N-homocysteinylation in elastin fiber maturation in mouse models (Cbs-KO, Mthfr-KO, and Pcft-KO). .

Selected Publications

• Sikora, M. Marczak L, Twardowski T, Stobiecki M, Jakubowski H. Direct monitoring of albumin lysine-525 N-homocysteinylation in human serum by LC/MS. Analytical Biochemistry. 2010;405(1):132-4. Epub 2010 Jul 5.
  
  
• Glowacki R, Bald E, Jakubowski H. Identification and origin of N-homocysteinyl-lysine isopeptide in humans and mice. Amino Acids. 2010 Nov;39(5):1563-9. Epub 2010 May 30.
  
  
• Perla-Kajan J, Jakubowski H. Paraoxonase 1 protects against protein N-homocysteinylation in humans. FASEB Journal. 2010 Mar;24(3):931-6. Epub 2009 Oct 30.
  
  
• Jakubowski H, Perla-Kajan J, Finnell RH, Cabrera RM, Wang H, Gupta S, Kruger WD, Kraus JP, Shih DM. Genetic or nutritional disorders in homocysteine or folate metabolism increase protein N-homocysteinylation in mice. FASEB Journal 2009;23:1721-7. Epub 2009 Feb 9.
  
  
• Jakubowski H, Boers GH, Strauss KA. Mutations in cystathionine beta-synthase or methylenetetrahydrofolate reductase gene increase N-homocysteinylated protein levels in humans. FASEB Journal 2008;22:4071-4076.