Krishna Sharma , PhD
Professor of Ophthalmology, Director of Research
E-mail: SharmaK@health.missouri.edu
Phone: (573) 882-8478
Fax: (573) 884-4100
Office: 213EC Mason Eye Institute
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.
Current Research
Areas: Structure-function of crystallins, role of ocular proteases and molecular
basis for cataract development.
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
Jaya Bhattacharyya, Ekaterina V. Shipova, Puttur Santhoshkumar,
K. Krishna Sharma
and Beryl J. Ortwerth. (2007) Effect of a Single AGE Modification on the Structure
and Chaperone Activity of Human alphaB-Crystallin. Biochemistry. 46 (50):14682-92.
Raju Murugesan, Puttur Santhoshkumar and
K. Krishna Sharma. (2007) Cataract-causing
AG98R mutant shows substrate-dependent chaperone activity. Mol. Vision, 13, 2301-9.
Puttur Santhoshkumar, Padmanabha Udupa, Raju Murugesan and
K. Krishna Sharma (2008)
Significance of interactions of low molecular weight crystallin fragments in lens
aging and cataract formation. J. Biol. Chem. 283 (13) 8477-8485.
Guruprasada Rao, Puttur santhoshkumar and
K. Krishna Sharma (2008) Anti-chaperone
A3/A1102-117 peptide interacting sites in human B-crystallin. Mol. Vision 14,
666-674.
