The process of generating proteins is extremely complicated. So are the structures of them. With the rapid development of technology, the analysis of proteins is essential to many fields such as genetics, pharmaceutics and so on. Carbohydrates are one of the most important of the constitution of proteins, which affect the space structures of them. Furthermore, it will affect the function of proteins.
The Introduction of Carbohydrate
Carbohydrate is the general name of polyhydroxy aldehyde or polyhydroxy ketone and its condensation and some derivatives, generally composed of carbon, hydrogen and oxygen three elements, widely distributed in nature. Carbohydrate is an important nutrient of human body. It is divided into three main categories: monosaccharide, disaccharide and polysaccharide. In general, monosaccharides and disaccharides are small (low molecular weight) carbohydrates, commonly known as sugar. For example, glucose is monosaccharide, sucrose and lactose are disaccharides.
Carbohydrates play an indispensable role in organisms. For instance, polysaccharides, like starch or glycogen can act as nutrients and cellulose consist of the cell walls of plant cell. It is also the backbone of some genetic material molecules, such as DNA and RNA. As early as 2000 years ago, the records of use of sugar was found in the Pre-Qin period of China.
The Process of Protein Synthesis
Protein synthesis refers to the process of biosynthesis of proteins according to the genetic information of the messenger RNA (mRNA) transcribed from DNA. There are many differences in the process of protein synthesis between prokaryotes and eukaryotes. The process of eukaryotes is more complex. Below will the process of protein synthesis in prokaryotes be introduced. Translation, the ribosome assembly of protein, is an important component of the biosynthetic pathway, with the generated messenger RNA (mRNA), the aminoacylation of translocation RNA (tRNA), and post-translational modification. Protein biosynthesis has been tightly regulated in many steps, and error checking mechanisms have been established.
Transcription refers to the transfer of genetic information from DNA to RNA, and the formation of a mRNA complementary to the DNA base sequence under the action of RNA polymerase.
Translation is the process of decoding the "base sequence" (nucleotide sequence) of the mature messenger RNA molecule (DNA through transcriptional) and generating the corresponding sequence of specific amino acids, according to the central rule of the genetic code.
3. Post-translational Modification：
Post-translational Modification refers to the chemical modification of the protein after translation. For most proteins, this is a later step in protein biosynthesis. In this process, a variety of functional group might be added to the specific polypeptide chain to extend the function of protein, among which post translational modification glycosylation is one of the main kinds of post translational modification. To study this intricate process, glycomics emerge as the times require, in which glycomics profiling is one of the key steps as the preparation of this study.
Glycosylation mainly refers to the enzymatic process that attaches glycans to organic molecules like proteins, lipids, or other. The most common form of glycosylation exists in the process of protein post-translational modifications (PTM). It is the one of the most challenging post-translational modifications, entailing a set of modifications instead of a single modification, which makes the profiling and analysis difficult. There are two normal kind of glycan that get involved in the process of post-translational modification, N- Glycan and O-Glycan.
1. N- Glycan：
N- Glycan is an oligosaccharide attached to the side chain amide nitrogen of the asparagine residue in the protein peptide chain. Such oligosaccharides typically have a core pentasaccharide and a similarly structured peripheral sugar chain. With the midst of the development of modern medical science, N-Glycan Analysis and N-glycan profiling is becoming more and more popular.
O-Glycan is an oligosaccharide attached to a serine in a protein peptide chain, as well as a side chain hydroxyl group of other amino acid residues. Most of these oligosaccharides are short and show different structures. Unlike N-glycans, there is no known O-linked amino acid consensus sequence yet and no universal enzyme can remove the majority of O-linked glycans so far, which makes O-Glycan profiling more difficult than N-glycan profiling.