Proteins, Proteins Everywhere
Gleeson, Frank, Pearson, Mark, The World and I
The massive undertaking to study the entire set of human proteins will clarify the molecular basis of many diseases, leading to more reliable diagnostics and more effective treatments.
Since the early 1990s, the Human Genome Project has been devoted to the scientific study of our genome--that is, the genetic material in a complete set of our chromosomes. The project's goal has been to identify all human genes, find their locations on the chromosomes, and discover their role in our lives. In so doing, it is helping us determine how various genes are associated with particular illnesses, such as cystic fibrosis, Alzheimer's disease, and forms of cancer. Likewise, other research efforts have undertaken detailed analyses of the genomes of various animals, plants, and microbes. As a result, public attention has been drawn to the field known as genomics.
On the molecular level, the genetic material consists of long, double- helical molecules of DNA (deoxyribonucleic acid) made from small building blocks (nucleotide pairs or base pairs). Genes are those segments of the DNA strands that encode molecules known as RNA (ribonucleic acid), many of which in turn act as templates for the synthesis of proteins. Thus the focus of the Human Genome Project has been to determine the precise sequence of base pairs in the DNA of each chromosome, and to identify the DNA segments that correspond to genes.
Considering that there are about 3 billion base pairs in the human genome, the task of sequencing them has been awesome. Yet, thanks to amazing developments in biotechnology and computing power, researchers have brought this task to near completion [see "Unraveling the Human Thread of Life," The World & I, September 2001, p. 136]. The number of protein-coding genes in the human genome is still unclear, but computer-assisted analyses of the DNA sequences have suggested that the figure is somewhere between 25,000 and 40,000.
Whatever the case, it is not the genes but the proteins they encode that are direct participants in most of our body functions. For instance, proteins in our muscles help us lift heavy loads; those in the eyes help create images of what we see; those in the brain process nerve impulses that allow communication with the rest of the body. Many proteins, known as enzymes, act as catalysts for various cellular reactions; others contribute to the structures of our tissues and organs. Some proteins are hormones, carrying signals between distant body parts; others are antibodies that fight infectious agents. On the other hand, if a gene is mutated, it may direct the synthesis of a defective protein, which may then lead to an illness.
Thus, to understand how our body operates in health and disease, we need to probe the elaborate functions of proteins. Given their tremendous complexity and variety, past research has been restricted to examining them one at a time or in small clusters. Now, however, with the taste of success on the level of the human genome, and with continuing technological developments, biologists are willing to tackle the far more complicated challenge of investigating the full set of proteins in the body.
The entire collection of proteins encoded by the genome of an organism is known as the proteome, and the new frontier of research that involves the system-wide study of these proteins is called proteomics. The aim of proteomics is to identify all the proteins in the selected organism, find their structures, and determine what they really do.
The complexity of proteomics begins with the complexity of protein structure. While a piece of DNA is constructed from four types of nucleotides that are specifically paired to generate a double-helical shape, a protein is made from 20 types of building blocks (amino acids) that are strung together and elaborately folded. Each protein has a unique three-dimensional (3-D) structure that is based on (but not easily predictable from) the sequence of amino acids. …