How many proteins are there in humans

Abstract

On this stage, there is no consensus on the Science question: “How many proteins are there in humans”. But with the improved efficiency on proteomics separation and the development of mass spectrometry technique, the question about protein type and quantity in the human body can be answered in part. Via analyzing the changes in the type and quantity of protein, the alternations in functional level of body can be disclosed. For better comprehensive understanding, the study of number of proteins in the human body must be solved from the synthesis, processing, post-translational modification, and the main source of protein in the human body. This article summarized the relationship between the number of proteins and the number of genes in the human body based on current researches, combining the evolution of eukaryotic model organisms, gene coding, protein modification and current proteomics techniques development, it comprehensively analyzed the problem about how many protein species may exist in human body. Proteins are the direct performer of all kinds of life activities and only consist of 20 kinds of amino acids. However, by different length and arrangement and combination, the theoretically limited amino acids varieties indeed can form vast number of protein bank. Since proteins are derived from genomic DNA, researching the numbers of coding frame could be treated as the basis to calculate protein species. Gene is the blueprint of synthesizing protein. Maintaining accuracy and stability of gene translation is vital for the inheritance of life species, thus even tiny variation of gene sequence may induce proteins to be different structurally and functionally formed by transcription and translation. In the meantime, by comparing and analyzing the protein splicing and gene’s alternative splicing, we are aware that in protein splicing, new peptide bonds come into being: during splicing, precursor protein’s intein are excised and the extein on both sides bond together. Almost Inteins consist of 134–650 aa, and gene’s alternative splicing means starting from a mRNA precursor (pre-mRNA), fusing different exons and produce multiple types of mature mRNA splicing isotypes by different splicing patterns (select different splicing sites and combine). Understanding this process can lead to a grasp of difficulty about counting proteins. In addition, from proteins to the maturation of proteins, various modifications are involved, and other processes like the bioactive peptide in vivo enzymolysis. The complexity of human life process is not the result of the direct expression of gene, but also the modifications of proteins’ post-translation, which make one gene correspond to more than one protein, so endow more complexity to human’s whole life process. As for antibody-one big source in human body, multiple types of antibodies are generated during immunogenesis. Every kind of antibody is a novel protein, and in the process of antibody-secreting immune cells activation, proliferation and differentiation, different antibodies are produced because of different stimulus factors and antigens, and in theory one person may have more than 1011 types of antibodies. Apparently, it’s quite challenging to analyze the questions about how many proteins are inside human body from either genomics or proteomics directions, which lead us failed to figure out how many proteins are in human body. With the advance of new enrichment materials, high-performance separation method, novel mass spectroscopy and biointelligence algorithm, large-scale and high throughout protein analysis must be applicable, especially in aspects like scale analysis of post-translation modifications of proteins, precise siting of target and low-sensitive inspections. In the near future, we are probably able to have a deeper understanding on the biological meaning of protein’s diversity, which will progress the problem about how many proteins are in human body.