07.01.2014 Views

LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

CHAPTER 1<br />

INTRODUCTION<br />

(named due to amino acid conservation between the PIKK family members FRAP, ATR,<br />

and TRRAP), a phosphoinositide 3,4-kinase (PI3K) domain and a FAT carboxy-terminal<br />

(FAT-C) domain [64]. One function of the FAT domain may be to interact with the<br />

kinase domain to stabilize the carboxy-terminal region of the protein [65]. Bioinformatics<br />

analysis indicates that the amino-terminal portions of ATM, ATR, mTOR and, likely,<br />

DNA-PKcs are composed of multiple huntingtin, elongation factor 3, A subunit of protein<br />

phosphatase 2A and TOR1 (HEAT) repeats [66]. Each HEAT repeat is composed of two<br />

interacting, anti-parallel alpha helices linked by a flexible loop. The amino-terminal<br />

regions of the PIKK proteins, therefore, are predicted to consist of multiple, interacting<br />

HEAT repeats that form a massive, superhelical scaffolding matrix [66]. While the<br />

function of the HEAT repeat domain remains unknown, it is speculated that it could<br />

provide a surface for interactions with other proteins. The first indications of the overall<br />

shape and dimensions of the ATM protein have recently emerged. Single particle electron<br />

microscopic analysis reveals that ATM has a large “head” domain of approximately<br />

115Å by 75–140 Å, as well as a long “arm” structure that protrudes from the head region<br />

[67]. The overall shape of ATM is, thus, similar to that of the related protein, DNA-PKcs,<br />

at similar resolution [68]. Both proteins have the ability to interact with ends of doublestranded<br />

(ds) DNA[69-72], and this interaction may be facilitated by a conformational<br />

change that causes the arm region to wrap around the DNA [67]. From the low-resolution<br />

(30 Å) structure of ATM, it is speculated that the HEAT domain corresponds to the<br />

head structure and the carboxy-terminal kinase domain to the arm. However, elucidation<br />

of the precise molecular architecture of ATM will require a higher resolution structure.<br />

42

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!