Besides hemoglobin, what proteins are present in red blood cells?

Question

I knew that mature red blood cells (RBCs) lacked nuclei, but I wasn't aware until just now that they also lacked ribosomes and mitochondria. Most cells in the human body all contain a common laundry list of housekeeping proteins and RNAs (including mitochondrial proteins and ribosomal RNAs), but I guess RBCs lack a number of them. Do they still have all of the other organelles? Obviously hemoglobin (and to a lesser extent carbonic anhydrase) makes up a large portion of the dry weight of RBCs, but are other proteins still present? If so, what are their relative abundances?For example, do red blood cells have any of the normal metabolic (i.e. ATP producing) proteins? Obviously they don't have any of the TCA cycle proteins, but do they still have the glycolysis ones?

Answer 1

Do they still have all of the other organelles? Not compared to a standard cell. RBC's must be able to travel through very narrow capillaries in the circulatory system, so they have a substantial reduction in protein "machinery" used for cell division, etc. As for proteins that are still present in the RBC's:. they still retain a cytoskeleton and bilayer composed of proteins, as well as membrane bound transport proteins. The membrane composition itself is unique in that it must be flexible, plastic, and must adhere to other cells. It has 3 layers: the glycocalyx (exterior), lipid bilayer containing membrane bound proteins, and the membrane skeleton. They also still have the enzymes responsible for ATP synthesis via glycolysis as well as the enzymes necessary in the pentose phsphate pathway.

As for relative abundances of proteins, that is a topic requiring a paper publication. This paper here :

https://pubs.acs.org/doi/pdf/10.1021/acs.jproteome.7b00025

describes a quantitative analysis of RBC's using proteomics for identification. They lyse the RBC's, digest them with a number of different enzymes, and use Chromatography and mass spectrometry for quantitative analysis. Apparently they identified 2090 proteins in whole RBC's and quantitatively measured 450 of them. Hemoglobin is obviously the most abundant, and carbonic anhydrase comes in second. Here is a verbatim quote from page 2756:

"Peroxiredoxin-1, -2, and -6 (PRDX1, PRDX12, and PRDX16) occur with similar copy numbers. The next group of highly abundant proteins consists of biliverdin reductase B (BLVRB), which catalyzes reduction of methemoglobin, and catalase (CAT) and superoxide desmutase (SOD1), which protect from toxic effects of oxygen peroxide and radicals, respectively. Bisphosphoglycerate mutase (BPGM), the central enzyme of the Rapoport−Luebering cycle, is present at 1.6 million copies. BPGM converts 1,3-bisphosphoglycerate, which is formed by glycolysis, to 2,3-bisphosphoglycarate (2,3-BPG). The main role of 2,3-BPG is to shift the equilibrium of hemoglobin toward the deoxy state. Housekeeping enzymes glyceraldehydeP dehydrogenase (GAPDH) and deglycase (PARK7)29 are present at 1.4 and 0.7 million copies, respectively. Calcium binder S100A4 is present at about 2 million copies. Another enzyme found to be present at 2−3 million copies was αsynuclein. Notably, it has recently be reported that RBCs as the major source of α-synuclein in blood"