Linear epitope

In contrast, most antibodies recognize a conformational epitope that has a specific three-dimensional shape (tertiary structure).

Proteins are composed of repeating nitrogen-containing subunits called amino acids.

The linear sequence of amino acids that compose a protein is called its primary structure, which typically does not present as simple line of sequential proteins (much like a knot, rather than a straight string).

But, when an antigen is broken down in a lysosome, it yields small peptides, which can be recognized through the amino acids that lie continuously in a line, and hence are called linear epitopes.

In contrast, in immunohistochemistry where protein structure is preserved, antibodies that recognize conformational epitopes are preferred.