Neuroscience

Protein movement in cells hints at greater mysteries

A new imaging technique that makes it possible to match motor proteins with the cargo they carry within a cell is upending a standard view of how cellular traffic reaches the correct destination. The research, which focuses ...

Alzheimer's disease & dementia

In Alzheimer's research, scientists reveal brain rhythm role

In the years since her lab discovered that exposing Alzheimer's disease model mice to light flickering at the frequency of a key brain rhythm could stem the disorder's pathology, MIT neuroscientist Li-Huei Tsai and her team ...

Medical research

Figuring out Alzheimer's

One of the tasks of scientists' work is to explain how the world functions. Their research ideas may often seem unrealistic but, as it turns out, their research may truly help a great many of us.

Oncology & Cancer

Study shows how circulating tumor cells target distant organs

Most cancers kill because tumor cells spread beyond the primary site to invade other organs. Now, a USC study of brain-invading breast cancer cells circulating in the blood reveals they have a molecular signature indicating ...

Diseases, Conditions, Syndromes

Toxoplasmosis: Preventing mother-to-child transmission

Professor Maritza Jaramillo knows a thing or two about parasites—she has spent most of her life studying them. "During my bachelor's degree in Colombia, I did an internship at a lab specializing in parasitic infections. ...

Protein

Proteins (also known as polypeptides) are organic compounds made of amino acids arranged in a linear chain. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the genetic code specifies 20 standard amino acids, however in certain organisms the genetic code can include selenocysteine — and in certain archaea — pyrrolysine. Shortly after or even during synthesis, the residues in a protein are often chemically modified by post-translational modification, which alter the physical and chemical properties, folding, stability, activity, and ultimately, the function of the proteins. Proteins can also work together to achieve a particular function, and they often associate to form stable complexes.

Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells. Many proteins are enzymes that catalyze biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. Proteins are also necessary in animals' diets, since animals cannot synthesize all the amino acids they need and must obtain essential amino acids from food. Through the process of digestion, animals break down ingested protein into free amino acids that are then used in metabolism.

Proteins were first described and named by the Swedish chemist Jöns Jakob Berzelius in 1838. However, the central role of proteins in living organisms was not fully appreciated until 1926, when James B. Sumner showed that the enzyme urease was a protein. The first protein to be sequenced was insulin, by Frederick Sanger, who won the Nobel Prize for this achievement in 1958. The first protein structures to be solved were hemoglobin and myoglobin, by Max Perutz and Sir John Cowdery Kendrew, respectively, in 1958. The three-dimensional structures of both proteins were first determined by x-ray diffraction analysis; Perutz and Kendrew shared the 1962 Nobel Prize in Chemistry for these discoveries. Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation, electrophoresis, and chromatography; the advent of genetic engineering has made possible a number of methods to facilitate purification. Methods commonly used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, and mass spectrometry.

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