Editors: Jennifer Baker, Andrés Rivera Ruiz, and Madeline Barron
There is much to appreciate about the way our bodies keep themselves healthy through the array of different immune cell types and their related, yet distinct, methods of protecting us from sickness. From T cells conducting orchestrated attacks on foreign pathogens to B cells producing antibodies which stave off severe illness at the outset of an infection, these cells and their diverse functions resemble a set of chess pieces in the way that they each perform unique tasks in consort with one another to achieve a common objective. However, their goal is not necessarily victory over any one opponent, but rather against all challenges to the immune system, whether external viruses such as COVID-19, or from within, as is the case with cancer.
Editors; Noah Steinfeld, Tricia Garay, and Scott Barolo
A glance into any organic chemistry or biochemistry textbook reveals a dizzying variety of chemical compounds, reactions and mechanisms. It is not at all obvious why one particular class of reaction, the attachment and detachment of a phosphate group (PO43-) to molecules like nucleotides and proteins, is central to making the chemistry of life “go.”
Proteins: Not Just for Getting Swole, Brah
Figure 1. A phosphate ion. Note the negative charges.
Proteins are the working-class heroes of the cell: they get things done. A protein’s function is largely determined by its shape, which in turn is dictated by the linear sequence of chemically distinct amino acid subunits it is composed of. The rules of protein folding are astonishingly complex. Generally speaking, the reluctance of hydrophobic (“water-fearing”) amino acids to project outward into the watery cytoplasm is the primary determinant of protein shape, but electrostatic interactions between amino acid residues are also important. Phosphate groups have three negative charges, which means that when they are linked to or removed from a protein by specialized enzymes, they can dramatically modify its shape and stability, and therefore its function. The phosphorylation/dephosphorylation cycle operates like a switch to regulate protein behavior: add a phosphate and you get a violent Mr. Hyde protein; take it off and you get the amiable Dr. Jekyll.
Figure 2. Cellular homunculi don’t exist – decisions are made by integrating signaling inputs from the environment to effect changes in gene expression.
So where do we find phosphorylation in biochemistry? The answer is: pretty much everywhere! I will discuss two key examples. Firstly, phosphorylation is important in “cell signaling,” the sensing of messages from outside a cell and their incorporation into cellular decision-making. It’s worth observing that there isn’t anything we’d recognize as a brain in cells – decision-making is an emergent property of the integration of these signals, not the doing of a microscopic cellular homunculus pulling levers or “thinking.”
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