Article

The NMR structure of the murine DLC2 SAM domain reveals a variant fold that is similar to a four-helix bundle.

Department of Biology, York University, Toronto, Ontario, Canada. <>
BMC Structural Biology (Impact Factor: 2.1). 02/2007; 7:34. DOI: 10.1186/1472-6807-7-34
Source: PubMed

ABSTRACT The tumor suppressor DLC2 (Deleted in Liver Cancer -2) participates in cell signaling at the mitochondrial membrane. DLC2 is characterized by a SAM (sterile alpha motif) domain, a Rho GTPase activating protein (GAP) domain, and a START lipid transfer domain.
Towards understanding the function of DLC2, we have solved the NMR solution structure of the SAM domain. The DLC2-SAM domain structure reveals an atypical four-helix composition that is distinct from the five-helix SAM domain structures that have been determined to date. From structural alignments, helix 3 of the canonical SAM domain appears to be replaced by shorter, extended secondary structure that follows a similar path. Another difference is demonstrated by helices 1 and 2 that form a helical hairpin that is situated approximately parallel to the canonical helix 5.
The DLC2-SAM domain adopts a structure that is topologically more similar to an anti-parallel four-helix bundle than a canonical SAM domain. This alternate topology may allow the DLC2-SAM domain to interact with a novel set of ligands.

0 Bookmarks
 · 
76 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Gametocytes of the protozoan Plasmodium falciparum ensure malaria parasite transmission from humans to the insect vectors. In their development, they produce the abundant specific protein Pfg27, the function and in vivo molecular interactions of which are unknown. Here we reveal a previously unreported localisation of Pfg27 in the gametocyte nucleus by immunoelectron microscopy and studies with HaloTag and Green Fluorescent Protein fusions, and identify a network of interactions established by the protein during gametocyte development. We report the ability of endogenous Pfg27 to form oligomeric complexes that are affected by phosphorylation of the protein, possibly through the identified phosphorylation sites, Ser32 and Thr208. We show that Pfg27 binds RNA molecules through specific residues and that the protein interacts with parasite RNA-binding proteins such as EF1alpha and PfH45. We propose a structural model for Pfg27 oligomerisation, based on the sequence and structural conservation here recognised between Pfg27 and sterile alpha motif. This study provides a molecular basis for Pfg27 to establish an interaction network with RNA and RNA-binding proteins and to govern its dynamic oligomerisation in developing gametocytes.
    International journal for parasitology 12/2009; 40(6):663-73. · 3.39 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The α-splice variant of p73 (p73α), a homologue of the tumour suppressor p53, has close to its C terminus a sterile alpha motif (SAM), SAMp73, that is involved in protein-biomolecule interactions. The conformational stability of SAMp73 is low (∼5 kcal mol(-1)), although its thermal stability is high. To explain this high thermostability, we studied the dynamics of SAMp73 over a wide range of GdmCl (guanidine hydrochloride) concentrations and temperatures by NMR relaxation, NMR hydrogen-exchange (HX) and fluorescence lifetime approaches. The slowest exchanging residues of SAMp73 belong to the helical regions, and they did exchange by a global unfolding process. Moreover, SAMp73 was very flexible, with most of its amide protons affected by slow μs-ms conformational exchange. Within this time scale, the residues of SAMp73 with the largest exchange rates (R(ex)) were involved in binding with other molecules; therefore, the flexibility in the μs-ms range was associated with biological functions. As the [GdmCl] increased, the pico-to-nanosecond flexibility of the backbone amide protons raised, but it did so differently depending on the residue. We were able to obtain, for the first time, the linear [GdmCl]-variation of the local conformational entropies, m(S(i)), which ranged from 5.3 to 0.3 cal mol(-1) K(-1) M(-1), similar to those measured by using macroscopic techniques in other proteins. Conversely, the temperature dependence of the pico-to-nanosecond dynamics of the backbone amide protons of SAMp73 indicates that the flexibility of some residues decreased with the temperature; these results explain the high thermostability of the protein.
    Physical Chemistry Chemical Physics 06/2012; 14(29):10308-23. · 3.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The sterile alpha motif (SAM) for protein-protein interactions is encountered in over 200 proteins, but the structural basis for its interactions is just becoming clear. Here we solved the structure of the EphA2-SHIP2 SAM:SAM heterodimeric complex by use of NMR restraints from chemical shift perturbations, NOE and RDC experiments. Specific contacts between the protein surfaces differ significantly from a previous model and other SAM:SAM complexes. Molecular dynamics and docking simulations indicate fluctuations in the complex toward alternate, higher energy conformations. The interface suggests that EphA family members bind to SHIP2 SAM, whereas EphB members may not; correspondingly, we demonstrate binding of EphA1, but not of EphB2, to SHIP2. A variant of EphB2 SAM was designed that binds SHIP2. Functional characterization of a mutant EphA2 compromised in SHIP2 binding reveals two previously unrecognized functions of SHIP2 in suppressing ligand-induced activation of EphA2 and in promoting receptor coordinated chemotactic cell migration.
    Structure 01/2012; 20(1):41-55. · 5.99 Impact Factor

Full-text

View
0 Downloads
Available from