Proteins are large biological molecules consisting of one or more chains of amino acids (or polypeptides). The set of proteins expressed in a particular cell or cell type is known as its proteome. Proteins are essential parts of living organisms and participate in virtually every biological process. Proteins perform a vast array of functions and are thus sometimes referred to as the “workhorse” molecules of life. Proteins are often chemically modified by posttranslational modification, which alters their property and activity. Proteins often associate to form a protein complex and achieve a particular function. The genetic engineering has made it possible to produce recombinant proteins in large quantities for research and clinical applications. 

 

 

 

 

 

 

 

Protein Classification

 

The human proteome are encoded by ~20,000 genes, which make up only 1–2% of our genome. Proteins can be broadly divided into three main classes: globular proteins, fibrous proteins, and membrane proteins according to their structural features. Most globular proteins are soluble and many of them are enzymes. Fibrous proteins are often structural, such as collagen – the major component of our connective tissues. Membrane proteins often serve as the receptors or channels for specific extracellular molecules to help them transmit signals or pass through the cell membrane. Many membrane proteins play important roles in cell signaling, immune responses, cell adhesion and migration as well as many other pathways.

 

 

 

 

Proteins can also be classified by the class and function as well as the biological process & pathway they participate in (see the pie chart above for an example for the classification of human proteome by class).  Among total 22340 proteins encoded by our genome,  about 37% (8309) are enzymes, which represent the most abundant class of proteins, including hydrolase, transferase, oxidoreductase, protease, kinase, ligase, phosphatase, lyase and isomerase. About 22% (4885) are regarded as membrane proteins, including cell junction protein, receptor, transporter, cell adhesion molecule, extracellular matrix protein, membrane traffic protein and transmembrane receptor regulatory/adaptor protein. There are 2724 (~12%) of nucleic acid binding proteins and 2041 (~9%) of transcription factors.  Interestingly only ~6% (1286) are cytoskeletal and structural proteins.

 

 » Go to the next topic: Post Genomic Recombinant Protein Expression

 

» Go to the next topic: Post Genomic Recombinant Protein Purification

 

« Return to Technical Support mainpage