The goal of this study was determining the structural organization peculiarities of the ORF2 and ORF3 proteins of the bovine immunodeficiency virus (BIV). Five ORFs were determined for two BIV isolates with complete genome using the ATGpr software, which permits effective prediction of translation initiation codons with nucleotide accuracy. Phyre2 software was used to predict, analyze the secondary structure and function of proteins. PONDR-FIT software was used to search for protein fragments in a disordered or natively unfolded state. Analysis of the amino acid composition of ORF2 and ORF3 proteins of BIVisolates regarding the presence of nonpolar, polar, aromatic, and hydrophobic amino acid residues was carried out using PSIPRED software. Models of the 3D-structure of proteins were obtained by I-TASSER server. 14% of α helices, 17% of β strands and 43% of disordered structure are predicted for the ORF3 protein. 37% of α helices, 0% of β strands, and 41% of disordered structure were determined for Gag polyprotein, which is translated from ORF2. The distribution of charged amino acid residues characterizes the surface properties of proteins. Their number reaches 23.9% for ORF2 protein. The amount of Arg is 5.2%, Lys — 8.0%, Glu — 7.3%, Asp — 3.4%. The total number of charged amino acid residues of ORF3 is 23.3%. The number of Arg is 12.6%, Lys — 4.9%, Glu — 1.9%, Asp — 3.9%. Only two ORFs of five ones coincide in nucleotide length (and, therefore, in length of corresponding proteins) for the two BIV isolates. The ORF3 protein belongs to the intrinsically disordered proteins that cannot be stably folded into a unique three-dimensional structure under physiological conditions, and the Gag polyprotein, which is translated from ORF2, belongs to the class of fully structured proteins. The secondary structure of both proteins shows the presence of α-helices
Keywords: polyprotein Gag, Lentivirus, Retroviridae
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