PDBsum entry 1awe

Signal transduction

PDB id

1awe

Contents

			Protein chain

					130 a.a.

References listed in PDB file

Key reference

Title

The solution structure of the pleckstrin homology domain of human sos1. A possible structural role for the sequential association of diffuse b cell lymphoma and pleckstrin homology domains.

Authors

J.Zheng, R.H.Chen, S.Corblan-Garcia, S.M.Cahill, D.Bar-Sagi, D.Cowburn.

Ref.

J Biol Chem, 1997, 272, 30340-30344. [DOI no: 10.1074/jbc.272.48.30340]

PubMed id

9374522

Abstract

A large subset of pleckstrin homology (PH) domains are immediately to the C terminus of diffuse B cell lymphoma (Dbl) homology (DbH) domains. Dbl domains are generally considered to be GTPase-exchange factors; many are proto-oncogenes. PH domains appear to function as membrane-recruitment factors, or have specific protein-protein interactions. Since dual domain (DbH/PH) constructs are known to have significant properties in other pathways, it is possible that a defined interdomain relationship is required for DbH/PH function. We determined the solution structure of the human SOS1 PH domain for a construct partially extended into the preceding DbH domain. There are specific structural contacts between the PH and the vestigial DbH domain. This appears to involve structural elements common to this subfamily of PH domains, and to DbH domains. The human SOS1 PH domain binds to inositol 1,4,5-triphosphate with a approximately 60 mu M affinity. Using chemical shift titration, the binding site is identified to be essentially identical to that observed crystallographically for the inositol 1,4,5-triphosphate complex with the PH domain of phospholipase Cdelta. This site may serve as an interdomain regulator of DbH or other domains' functions. While the overall fold of the human SOS1 PH domain is similar to other PH domains, the size and position of the intrastrand loops and the presence of an N-terminal alpha-helix of the vestigial DbH domain suggest that the subfamily of PH domains associated with DbH domains may be a well defined structural group in which the PH domain is a membrane recruiter and modulator.



	Figure 1. Fig. 1. Sequential organization of SOS and its four homology segments. A, the hSOS1 sequence (10) contains a DbH domain (5), followed by a PH domain (reviewed in Shaw (1)), an intervening stretch (551-793), the CDC25 Ras-activating domain, and a proline-rich segment (PP), associated with Grb2 binding (30). The sequence^ expressed and structurally determined here is the gray patch. B, structure-based alignment of PH domains using pairwise superposition of the structures and direct calculation of aligned RMSDs, based^ on elements of secondary structure, optimized by addition of deletion of individual residue pairs. Structures are hSOS1 (this work), GRK-2/ ARK-1 (D. Fushman, T. Najmaabadi-Haske, S. Cahill, J. Zheng, H. LeVine III, and D. Cowburn, J. Biol. Chem., in press), dynamin (31), spectrin (18), pleckstrin (24), and PLC (15). The^ color coding corresponds to the secondary structure elements in Fig. 2 and the binding site are marked in red and underlined. C, predicted helical segments of the DbH domain of hSOS1, using programs DSC (17). The numbers in blocks below the sequence, labeled P_H at the left, are the deciles of the probability that the individual residue is in an -helix. D, alignment of the C-terminal segment of multiple DbH domains, and the predicted C-terminal -helical portion. The program CLUSTAL W (32) was used to perform the multiple alignment. Sequences are (GI = GenBankTM accession no.) CDC24 (GI1345705), DBL (GI118279), ECT2 (GI423597), FGD1 (GI1706789), LBC (GI458210), LFC (GI1582805), LSC (GI1389756), OST (GI1083745), RasGRF (GI1083745), TIAM1 (GI897557), TIM (GI484102), and VAV (GI586213) P[lwen]H, the decile of the^ probability that the individual residue in part of an -helix (16).		Figure 2. Fig. 2. Structural representations of the determined solution structure of hSOS1 PH domain. A, overlap of 20 structures with the lowest target functions. In panels A-C, blue indicates an -helical secondary structural element, yellow indicates the first -sheet, and green the second. The RMSD (Å) for the ensemble of^ 20 lowest target function structures are, for the backbone heavy atoms (C , N , C ) in the secondary structure elements, residues 446-453 ( 1), 457-464 ( 2), 467-471 ( 3), 490-494 ( 4), 498-504^ ( 5), 512-518 ( 6), 522-528 ( 7), 531-548 ( C), 0.33 Å, for all atoms in the secondary structures is 1.18 Å, for all backbone^ heavy atoms is 1.4 Å, and for all atoms is 2.16 Å. Note the well defined secondary structural elements, and the highly variable^ loops. B, ribbon trace of one structure of A. The orientation is identical to that of A. C, ribbon trace of the same structure^ as in B rotated about the C- helix axis, to show the specific^ relationship of the N-terminal -helix to loop 3/4. There are^ 50 NOE distance constraints between the N-terminal part (422-433) to the rest of the protein (446-551). Five strong and absolutely unambiguous NOEs between backbone protons are indicated in gray between the two substructures and are (from top to bottom), Asn428 H -Ala^486 H (nominal upper limit NOE, 2.9 Å), Asn428 H -Glu487 HN (3.23 Å), Ile^429 HN-Tyr488 HN (5.0 Å), Asp430 HN-Leu490 HN (4.14 Å), and Asp430 H -Arg489 H (3.47 Å). D, grasp (14) charge surface of the SOS PH domain, in the orientation of panels A and B.

PROCHECK

	Headers