Krishna K. Sharma

Professor of Opthalmology

Email:	sharmak@missouri.edu
Phone:	(573) 882-8478
Fax:	(573) 884-4100
Office:	213 Eye Clinic
Mailing Address:	213EC Mason Eye Institute One Hospital Drive University of Missouri-Columbia Columbia, MO 65212
Research Areas:	Structure-function of crystallins, role of ocular proteases and molecular basis for cataract development.

Educational Background

BS	University of Mysore	India	Biology/Chemistry
MS	University of Mysore	India	Biochemistry
PhD	University of Mysore	India	Biochemistry

Notable Honors and Service

Robert E. McCormick Scholar Award from Research to Prevent Blindness in 1999.
Cataract Research Award from National Foundation for Eye Research in 2000
Lew R. Wasserman Merit Award from Research to Prevent Blindness in 2002
Program Committee Chair for Lens Section, Annual Meeting of Association for Research in Vision and Ophthalmology in 2007

Research Description

The lens of the eye is an excellent model for studying the effects of aging. The lens is primarily composed of long-lived highly stable proteins called crystallins. The normally transparent lens often gradually becomes cloudy with aging, leading to cataract formation. Cataract is a major cause of blindness worldwide. By age 80, more than half of Americans either have a cataract or have had cataract surgery. Cataract primarily develops as a result of extensive modification, aggregation and precipitation of the lens proteins called crystallins. In our studies of the molecular mechanisms of cataract formation, we are investigating the role of cellular enzymes called proteases in cataractogenesis and the structure and function of the major lens crystallin, alpha-crystallin.

Every cataract lens analyzed thus far in laboratories across the world has exhibited evidence of proteolysis (the degradation of crystallin proteins). However, the specific proteases responsible for the proteolysis of lens crystallins and the subsequent alteration in their properties are yet to be characterized. Using specific peptide substrates that mimic the in vivo cleavage sites in crystallin, we have demonstrated in lens extracts the presence of proteases that may be responsible for the breakdown of lens proteins. We are now focusing on the isolation and complete characterization of these proteases. The results of these studies will enable us to develop strategies to control the crystallin degradation in vivo, which may eventually lead to the development of interventions to prevent cataract formation.

The human lens expresses acylpeptidehydrolase, a member of the unique high-molecular weight serine peptidases. We are investigating the role of this protease in lens proteolysis. We have found that cataract develops in mice that overexpress this protease. The lenses from these animals show the accumulation of specific peptides. To understand the role of these peptides in cataract formation, we are now investigating the source of these peptides and the interaction of these peptides with crystallins.

The crystallins account for approximately 95% of lens proteins. There are three types of lens crystallins: alpha, beta and gamma. Alpha crystallin is a protein aggregate with a molecular weight of about 800 kDa. It is formed by the subunits A and B, each with a molecular weight of 20 kDa. These subunits have high sequence homology to small heat shock proteins. They display chaperone-like properties. The chaperone-like properties of alpha-crystallin (and its subunits) are likely to play a significant role in preventing the protein aggregation and light scattering that are associated with clouding of the lens, thereby helping to maintain lens transparency. Studies in our laboratory are directed toward the identification of the chaperone sites in both A and B subunits of alpha-crystallin and the characterization of the chemical modifications that occur at these sites and affect the chaperone activity of alpha-crystallin. We have also chemically synthesized to peptides, called mini-alpha A-crystallin and mini-alpha B-crystallin, and have shown that these peptides possess the antiaggregation properties of molecular chaperones. The availability of mini-alpha A and mini-alpha B gives us an opportunity to investigate the structural requirements of the chaperone site as well as the conformational specificity (structure or shape) of target proteins during chaperone action. This information will help us understand the mechanisms for maintaining lens transparency and the changes that occur to make the lens become cloudy.

While the primary sequence of alpha-crystallin subunits has been known for many years, the tertiary and quaternary organization of alpha-crystallin remains unknown. The structural organization of alpha-crystallin and the interaction of A and B subunits in alpha-crystallin aggregate are other areas of study in our laboratory. We are using site-directed cysteine mutations to study the A and B subunit contact sites in alpha-crystallin. Understanding the structural organization and interaction of A and B subunits will help us learn how cataracts develop and how they can be prevented.

Selected Publications

R. Senthil Kumar, Raghothama Chaerkady and K. Krishna Sharma (2002). Characterization of anti-chaperone peptides derived from beta L-crystallins. J. Biol. Chem. 277, 39136-39143

P. Santhoshkumar and K. Krishna Sharma (2004) Inhibition of amyloid fibrillogenesis and toxicity by a peptide chaperone. Mol. and Cell. Biochem. 267, 147-155.

Y. Sreelakshmi, P. Santhoshkumar, J. Bhattacharyya and K. Krishna Sharma (2004) alpha A-crystallin interacting regions in the small heat shock protein, alpha B-crystallin. Biochemistry, 43, 15785-15795.

Jaya Bhattacharyya, Padmanabha Udupa, Jing Wang and K. Krishna Sharma (2006) Synthesis and characterization of mini-alpha B-crystallin chaperone. Biochemistry 45, 3069-3076.

Y. Sreelakshmi and K. Krishna Sharma (2006) The interaction between alpha A- and alpha B-crystallin is sequence-specific. Mol. Vision 12, 581-587.

A. Aziz, P. Santhoshkumar, K. Krishna Sharma, E.C. Abraham. (2007) Cleavage of the C-Terminal Serine of Human alpha A-Crystallin Produces alpha (1-172) with Increased Chaperone Activity and Oligomeric Size. Biochemistry, 46(9):2510-2519

Employment Opportunities

Post-Doctoral Opportunities

Electronic submission is encouraged, e-mail to biochemsearch@missouri.edu

Applicants should send CV and names of two references to:
Dr. Krishna Sharma
Postdoctoral Application
213EC Mason Eye Institute
One Hospital Drive
University of Missouri-Columbia
Columbia, MO 65212

Structure-function of crystallins, role of ocular proteases and molecular basis for cataract development.