While HIV MA proteins associate in solution and

The myristoyl switch [21]. While HIV MA proteins associate in solution and in crystal structures as trimers, they organize onto membranes in a hexamer arrangement [26]. These observations have led to the suggestion that the MA trimers incorporate into Gag hexamers, with the trimers forming nodes that interconnect the hexamers [27]. Previous studies have determined the three-dimensional structure n-Phenylpiperazine-1-carboxamide of HIV p17, SIV p17 and EIAV p15 by nuclear magnetic resonance spectroscopy (NMR) [21,28-30] and X-ray crystallography [13,31,32]. MA proteins appear to be globular proteins with a compact fold made of five -helices. In addition, the HIV protein contains a highly basic platform, which allows the targeting of Gag polyproteins to the plasma membrane [14,15]. These structural studies have also demonstrated that p17 HIV and p17 SIV can form trimers [13,32]. However, some retroviral matrix proteins, such as EIAV MA, are dimerunits in crystal structures [31,33]. In fact, these conformational differences between the lentiviral proteins may be correlated with their mode of association. Hatanaka et al. suggested that the dimeric conformation observed for EIAV p15 could correspond to a weakened membranebinding state and proposed a new alternative membranebinding mechanism [31]. The comparison of the atomic structure of FIV p15 with those of matrix proteins of other retroviruses, such as HIV or EIAV, will help to define the specificity of the molecular mechanisms of FIV assembly. To characterize the FIV p15 structure, we over-expressed FIV p15. This allowed us to perform the first studies on the oligomeric state of the FIV p15 protein and to determine the crystal structure of full-length FIV p15. The structure of a C-terminal-truncated FIV p15 was solved in turn to assess the role of this region in the oligomerization process. In conclusion, we discuss the conformational differences observed between FIV p15 and the matrix protein of other lentivirus. In addition, 8-tetrahydronaphthalen-1-yl)acetamide 1-(Trifluoromethyl)-4-vinylbenzene 3-Chloro-2-oxopropyl acetate 4-Fluoro-3-iodobenzoic acid 7-Nitro-3 we also discuss the possible role of the flexible C-terminus of FIV p15 in the replication cycle.ResultsBiochemical and biophysical characterization of the FIV p15 oligomeric stateRetroviral matrix proteins oligomerize into dimers, trimers or hexamers [21,26,31]. Thus, we evaluated the oligomerization properties of FIV p15. The FIV p15 protein was analyzed by DLS (dynamic light scattering) to determine its oligomerization state in solution at different concentrations (3 mg/ml and 6 mg/ml) and pH values (pH 6 and pH 7.4) (Figure 1A). A single peak was observed in each experiment, which confirmed the homogeneity of the protein solution. At 6 mg/ml, the average diameter of the FIV p15 protein in 50 mM sodium phosphate pH 7.4 was 4.3 nm with a standard deviation of 0.2 nm (Figure 1A). This PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/13867361 value is consistent with a monomeric form of FIV p15 [34]. In contrast, the protein in 50 mM MES pH 6 presented an average diameter of 5 nm and a standard deviation of 0.1 PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/14445666 nm (Figure 1A), suggesting that the protein was mainly in its dimeric form at 6 mg/ml in this more acidic buffer. This was confirmed by cross-linking experiments on the same samples using bis(sulfosuccinimidyl)suberate (BS3). These experiments demonstrated that the FIV p15 protein in 50 mM sodium phosphate pH 7.4 was mainly monomeric, whereas a dimeric state was observed for the protein in 50 mM MES pH 6 (Figure 1B). These 4-((2-Hydroxyethyl)(methyl)amino)benzaldehyde results are in a good agreement with our experimental data obtained by DLS. It is noteworthy that the protein was monomeric i.