What We Know

How do scientists diagram (draw) protein structures?

Here's an example of how primary structure. We use a colored letter code to show part of the ordering of two different digestive enzymes (enzymes are proteins that facilitate chemical reactions of organic compounds).

--------------ANTPORLQQASLPLLSNTNCKK---------- Enzyme A

--------------GQLAQTLQQAYLPTVDYAICSS---------- Enzyme B

Amino Acid Key: A = alanine C = cysteine D = aspartic acid I = isoleucine G = glycine K = lysine L = leucine N = asparagine P = proline Q = glutamine R = arginine S = serine T = threonine V = valine Y = tyrosine

Note that the LQQA sequence is common to both proteins. When the entire sequence of these two proteins is considered, there is about 40% overlap of identical sequences.

Here's how scientists visualize higher-order structures

Amino acids that have no electric charge avoid water and are attracted to lipid and each other. As a result, they form a coil. So, to simplify the representation of those sections of a protein, they are shown as a coiled ribbon (see diagram on right).

The illustration below represents the combined result of coiling and folding of a protein when it gets embedded in a membrane.

Combined Result of Folding and Coiling In a Membrane Image

This picture shows two ways of drawing a membrane protein. Left: secondary coiled structure, with the coiled part buried in the membrane. The small letters are the first letter of names of the amino acids, showing the sequence as we explained at the top of this page. Middle: a "ribbon" diagram" of the same thing, with the red parts representing uncoiled amino acid strands that are outside of the membrane. Far right: diagrams showing how the structure might look if you were looking down on the membrane rather than looking at it from the side. Photograph courtesy of Dr. Fillipp Oesterhelt, University of Munich, Germany.