A nucleoprotein It is any type of protein that is structurally associated with a nucleic acid - either RNA (ribonucleic acid) or DNA (deoxyribonucleic acid). The most prominent examples are ribosomes, nucleosomes, and nucleocapsids in viruses..
However, any protein that binds to DNA cannot be considered a nucleoprotein. These are characterized by forming stable complexes, and not a simple transient association - like the proteins that mediate DNA synthesis and degradation, which interact momentarily and briefly..
The functions of nucleoproteins vary widely, and depend on the group to be studied. For example, the main function of histones is the compaction of DNA into nucleosomes, while ribosomes participate in the synthesis of proteins..
Article index
Generally, nucleoproteins are made up of a high percentage of basic amino acid residues (lysine, arginine and histidine). Each nucleoprotein has its own particular structure, but all converge to contain amino acids of this type.
At physiological pH, these amino acids are positively charged, which encourages interactions with the molecules of genetic material. Next we will see how these interactions occur.
Nucleic acids are made up of a backbone of sugars and phosphates, which give them a negative charge. This factor is key to understanding how nucleoproteins interact with nucleic acids. The bond between proteins and genetic material is stabilized by non-covalent bonds.
Likewise, following the basic principles of electrostatics (Coulomb's law), we find that charges of different signs (+ and -) attract.
The attraction between the positive and negative charges of the proteins and the genetic material gives rise to non-specific interactions. In contrast, specific junctions occur in specific sequences, such as ribosomal RNA..
There are different factors that are capable of altering the interactions between the protein and the genetic material. Among the most important are the concentrations of salts, which increase the ionic strength in the solution; ionogenic surfactants and other chemical compounds of a polar nature, such as phenol, formamide, among others.
Nucleoproteins are classified according to the nucleic acid to which they are attached. Thus, we can distinguish between two well-defined groups: deoxyribonucleoproteins and ribonucleoproteins. Logically, the former target DNA, and the latter RNA.
The most prominent function of deoxyribonucleoproteins is the compaction of DNA. The cell faces a challenge that seems almost impossible to overcome: properly winding almost two meters of DNA into a microscopic nucleus. This phenomenon can be achieved thanks to the existence of nucleoproteins that organize the strand.
This group is also associated with regulatory functions in the processes of replication, DNA transcription, homologous recombination, among others..
Ribonucleoproteins, for their part, fulfill essential functions, which range from DNA replication to the regulation of gene expression and regulation of the central metabolism of RNA..
They are also related to protective functions, since messenger RNA is never free in the cell, because it is prone to degradation. To avoid this, a series of ribonucleoproteins associate with this molecule in protective complexes..
The same system is found in viruses, which protect their RNA molecules from the action of enzymes that could degrade it.
Histones correspond to the protein component of chromatin. They are the most prominent within this category, although we also find other proteins bound to DNA that are not histones, and are included in a large group called non-histonic proteins.
Structurally, they are the most basic proteins in chromatin. And, from the point of view of abundance, they are proportional to the amount of DNA.
We have five kinds of histones. Its classification was based, historically, on the content of basic amino acids. Histone classes are practically invariable among eukaryotic groups.
This evolutionary conservation is attributed to the enormous role that histones play in organic beings.
In case the sequence that codes for any histone changes, the organism will face serious consequences, since its DNA packaging will be defective. Thus, natural selection is responsible for eliminating these non-functional variants.
Among the different groups, the most conserved are histones H3 and H4. In fact, the sequences are identical in organisms as far apart - phylogenetically speaking - as a cow and a pea..
DNA coils itself into what is known as the histone octamer, and this structure is the nucleosome: the first level of compaction of genetic material..
Protamines are small nuclear proteins (in mammals they are composed of a polypeptide of almost 50 amino acids), characterized by having a high content of the amino acid residue arginine. The main role of protamines is to replace histones in the haploid phase of spermatogenesis.
These types of basic proteins have been proposed to be crucial for the packaging and stabilization of DNA in the male gamete. They differ from histones in allowing denser packing.
In vertebrates, from 1 to 15 coding sequences for proteins have been found, all grouped on the same chromosome. Sequence comparison suggests that they have evolved from histones. The most studied in mammals are called P1 and P2.
The most conspicuous example of proteins that bind to RNA is in ribosomes. They are structures present in virtually all living things - from small bacteria to large mammals.
Ribosomes have the main function of translating the RNA message into an amino acid sequence.
They are a highly complex molecular machinery, made up of one or more ribosomal RNAs and a set of proteins. We can find them free within the cell cytoplasm, or anchored in the rough endoplasmic reticulum (in fact, the “rough” aspect of this compartment is due to ribosomes).
There are differences in the size and structure of ribosomes between eukaryotic and prokaryotic organisms..
Yet No Comments