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Dr. Lalima Ahuja

Room: 
MoSE 3201A
Date: 
Thursday, February 14, 2019 - 4:00pm to 5:00pm
Allosteric regulation of proteins in phosphorylation-based signaling pathways

 

Phosphorylation based signaling forms the cornerstone of our present understanding of human physiology
and disease. Reversible phosphorylation of hydroxyl-groups of Serine, Threonine and Tyrosine residues
is achieved by the intense balancing roles of the phosphorylating Protein Kinase and the
dephosphorylating Protein Phosphatase enzymes (1). Specialized phosphate-binding modules and pseudoenzyme
forms of Protein Kinases and Protein Phosphatases also participate in this realm and add an
additional layer of signaling regulation. Protein allostery based mechanisms of regulation play a crucial
role in maintaining the biological function of all these proteins. In my career path I have been fortunate to
work on both sides of the signaling balance; viz., the Protein Kinases and the Protein Tyrosine
Phosphatases.

Protein Tyrosine Phosphatases (PTP), especially their bi-domain forms are an intriguing system where
two conserved PTP domain occur in tandem but only one of them has phosphatase activity (2). The role
of the silent domains is understudied but finds crucial relevance in human disease, where the ‘silent’
features of these domains remain unexplored. The canonical PTP phosphatase domain has been
extensively characterized and a complete structural explanation of its catalytic cycle is available (3). We
appreciate the determinants of modulated PTP domain activity and the need of the hour is to extend this
work on the PTP domains of other versatile systems. These include understanding the role of pseudophosphatases
in axonal guidance, cancer and host-pathogen interaction etc. A major focus of my
laboratory will be on characterization of such unexplored bi-domain PTP phosphatases, including PTP
relevant in Parkinson disease and the pseudo-PTP domains of IA2 and IA2β implicated in insulin granule
turnover of the human pancreas.

Eukaryotic Protein Kinases (EPKs) are a large family of enzymes with about 540 members. Their
expertise lies in working as molecular switches that must be turned-on only in the needs of the cell.
Extensive regulation is required for their modulated function and many mechanism are set in place to
achieve protein specificity (4). Allosteric regulation is crucial and synonymous with regulation of EPKs
(5). The role of metal ions as the Kinase active site regulate its mechanisms from Michaelis-Menten to
Single-turnover kinetics (6, 7). While much work is done on EPKs; their diverse signaling and regulatory
mechanisms continue to pose fresh challenges. Especially the role of distal mutations effecting the kinetic
activity of these proteins continues to be an intriguing subject of study (8). The role allosteric effects in
regulation of kinetic properties of EPKs is explored using unique and novel computational methods in
combination with traditional biochemical techniques. These studies have allowed for the formulation of a
‘String Theory’ based explanation of protein entropy and its effect on the EPK catalytic cycle (8). In my
laboratory, I would like to extend these novel concepts to enable us to study the silent Pseudo-kinase
domains including those of JAK Kinases to explore the role of dimerization-independent allostery in these
proteins. I shall be also focusing on the atypical EPK domains of PKC proteins that regulate cell polarity
and are important targets for cancer therapy.

1. Ahuja LG (Protein tyrosine phosphatases : structure, signaling and drug discovery. p 1 online resource.
2. Ahuja LG & Gopal B (2014) Bi-domain protein tyrosine phosphatases reveal an evolutionary adaptation to optimize signal
transduction. Antioxid Redox Signal 20(14):2141-2159.
3. Madan LL & Gopal B (2011) Conformational basis for substrate recruitment in protein tyrosine phosphatase 10D.
Biochemistry 50(46):10114-10125.
4. Shaw AS, Kornev AP, Hu J, Ahuja LG, & Taylor SS (2014) Kinases and pseudokinases: lessons from RAF. Mol Cell Biol
34(9):1538-1546.
5. Hu J, et al. (2015) Kinase regulation by hydrophobic spine assembly in cancer. Mol Cell Biol 35(1):264-276.
6. Knape MJ, et al. (2015) Divalent Metal Ions Mg2+ and Ca2+ Have Distinct Effects on Protein Kinase A Activity and Regulation.
ACS Chemical Biology 10(10):2303-2315.
7. Zhang P, et al. (2015) Single Turnover Autophosphorylation Cycle of the PKA RIIbeta Holoenzyme. PLoS Biol 13(7):e1002192.
8. Ahuja LG, Kornev AP, McClendon CL, Veglia G, & Taylor SS (2017) Mutation of a kinase allosteric node uncouples dynamics
linked to phosphotransfer. Proc Natl Acad Sci U S A 114(6):E931-E940.

Contact Information: 
Prof. Amit Reddi (amit.reddi@chemistry.gatech.edu)
Map of Georgia Tech

School of Chemistry & Biochemistry

901 Atlantic Drive Atlanta, GA 30332-0400

(404) 894-4002 (phone) | (404) 894-7452 (fax)