Abundant perithecial protein: Difference between revisions

The two domain structure of APP consists of the N-terminal domain, being a beta gamma-crystallin, and the Ig-like domain located at the C-terminus. Each domain interacts with the other to form a tightly coiled protein. Likely, APP is not able to bind to Ca2+ due to the near-identical structure of half the N-terminus and the core of each domain. The Ca2+ coordinating residues of APP will reconform into loops 1 and 2 in the second greek motif, N/D-N/D-X1-X2-ST/S motif and the beta hairpin. Met121 is localized to the surface of APP, though it does not play a role in major interactions of APP, except for the hydrogen bonds which mediate Glu60 of the main carbon chain. APP does not provide Ca2+ densities in crystallization, though crystals have been identified in the presence of 10-30mM CaCl2. Overall, APP fails to provide statistics associated with Ca2+. In APP, the primary carbonyl oxygen, in the second hairpin, of Gln56 coordinates the positive x-position in APP-NTD is relocated from 6.7 Å in APP-NTD and rotate toward the Ig-like domain, and away from the alternative Ca2+ binding site. Likewise, the hydroxyl group of Ser81 relocated 3.5 Å further from the Ca2+ binding site of APP-NTD. Further, the orientation of Gln56 primary chain and the side chain of Ser81 as located in APP will degenerate the APP Ca2+ binding site. Further, Asp39 coordinates with the negative x-position, and also shifts 3.1 Å. This distance spanning the two molecules is 14 Å with respect to APP, and is 4.7 Å when APP-NTD is bound with Ca2+. The exaggerated shifts in distance between the two molecules is significant, considering the radius of gyration (Rg) of 11.8 combined with a particle dimension (Dmax) of 40.2 Å. Overall, the 3D structure of APP is largely culprit of its inability to bind Ca2+, where the residues residing within the Ca2+ binding site in APP-NTD are unalike those of APP, further promoting the disability of the Ca2+ binding site of the parent APP.

== References ==