Detection of Hypermodified Middle-Envelope (M) Proteins Secreted from Naturally Occurring HBV Variants Containing a preS2 Internal Deletion
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Human hepatitis B virus (HBV) produces three structurally related envelope proteins (also called surface antigens) from a single open reading frame (ORF) (Fig. 1 ). This ORF contains three in-frame translational initiation AUG codons, dividing it into three regions: preS1, preS2, and S (
1
,
2
). The three envelope proteins are referred to in the literature as large (L) (p39/gp42), middle (M) (gp33/gp36), and small (S, major surface antigen) (p24/gp27) envelope proteins. These proteins are co-carboxy-terminal proteins with different amino terminal extensions.
Fig. 1.
Cartoon illustration of three related large (L), middle (M), and small (S) HBV envelope proteins. The top box represents the entire envelope open reading frame divided into preS1, preS2, and S domains. Amino acids methionine at positions 1, 120, and 175 indicate the respective translational initiation sites for L, M, and S envelope proteins. Position 400 is the common termination site for all three envelope proteins. The letter “
a
” indicates the group
a
determinant, which is located between amino acids 298 and 322 and shared by all three envelope proteins. The symbol
represents N-linked complex glycans at asparagine (Asn) 123 and 320.
