Group-specific antigen
Videos
Group-specific antigen, or gag, is the polyprotein that contains the core structural proteins of an Ortervirus. It was named as such because scientists used to believe it was antigenic. Now it is know
HIV-1 Gag protein homo18-mer, Human immunodeficiency virus 1
Alpha helix
Videos
An alpha helix is a sequence of amino acids in a protein that are twisted into a coil.
Contrast of helix end views between α (offset squarish) vs 310 (triangular)
Ramachandran plot (φ, ψ plot), with data points for α-helical residues forming a dense diagonal cluster below and left of center, around the global energy minimum for backbone conformation.
An α-helix in ultrahigh-resolution electron density contours, with oxygen atoms in red, nitrogen atoms in blue, and hydrogen bonds as green dotted lines (PDB file 2NRL, 17–32). The N-terminus is at the top, here.
Leucine zipper coiled-coil helices & DNA-binding helices: transcription factor Max (PDB file 1HLO)