Nucleoproteins are conjugated with (either DNA or RNA).
Structures
Nucleoproteins tend to be positively charged, facilitating interaction with the negatively charged nucleic acid chains. The tertiary structures and biological functions of many nucleoproteins are understood.
[Graeme K. Hunter G. K. (2000): Vital Forces. The discovery of the molecular basis of life. Academic Press, London 2000, .][Nelson D. L., Cox M. M. (2013): Lehninger Biochemie. Springer, .] Important techniques for determining the structures of nucleoproteins include X-ray diffraction, nuclear magnetic resonance and cryo-electron microscopy.
Viruses
Virus genomes (either
DNA virus or
RNA virus) are extremely tightly packed into the
Capsid.
Many
are therefore little more than an organised collection of nucleoproteins with their binding sites pointing inwards. Structurally characterised viral nucleoproteins include influenza,
,
,
Bunyamwera virus,
Schmallenberg,
,
Crimean-Congo hemorrhagic fever,
and
Lassa virus.
Deoxyribonucleoproteins
A deoxyribonucleoprotein (DNP) is a complex of DNA and protein.
The prototypical examples are
, complexes in which genomic DNA is wrapped around clusters of eight
histone proteins in
Eukaryote cell nuclei to form
chromatin.
replace histones during spermatogenesis.
Functions
The most widespread deoxyribonucleoproteins are
, in which the component is
nuclear DNA. The proteins combined with DNA are
and
; the resulting nucleoproteins are located in
. Thus, the entire
chromosome, i.e.
chromatin in
eukaryotes consists of such nucleoproteins.
[Nelson D. L., Michael M. Cox M. M. (2013): Lehninger Principles of Biochemistry. W. H. Freeman, .]
In eukaryotic cells, DNA is associated with about an equal mass of histone proteins in a highly condensed nucleoprotein complex called chromatin.
Deoxyribonucleoproteins are also involved in homologous recombination, a process for DNA repair that appears to be nearly universal. A central intermediate step in this process is the interaction of multiple copies of a recombinase protein with single-stranded DNA to form a DNP filament. Recombinases employed in this process are produced by archaea (RadA recombinase),
Ribonucleoproteins
with DNA stained blue, and
Nucleolin in red. The nucleolin protein binds some
(e.g. mRNA for Interleukin-6). This protects those mRNAs from degradation by Kaposi's sarcoma-associated herpesvirus when infected. This RNA-nucleolin complex is then safely transported to the cytosol for translation by ribosomes to produce the Interleukin-6 protein, which is involved in antiviral immune response.
]]A
ribonucleoprotein (RNP) is a complex of
ribonucleic acid and RNA-binding protein. These complexes play an integral part in a number of important biological functions that include transcription, translation and regulating gene expression
and regulating the metabolism of RNA.
A few examples of RNPs include the
ribosome, the enzyme
telomerase, vault ribonucleoproteins,
RNase P,
hnRNP and small nuclear RNPs (
), which have been implicated in
pre-mRNA RNA splicing (
spliceosome) and are among the main components of the
nucleolus.
Some viruses are simple ribonucleoproteins, containing only one molecule of RNA and a number of identical protein molecules. Others are ribonucleoprotein or deoxyribonucleoprotein complexes containing a number of different proteins, and exceptionally more nucleic acid molecules. As of 2018, over 2000 RNPs can be found in the RCSB Protein Data Bank (PDB).
Furthermore, the Protein-RNA Interface Data Base (PRIDB) possesses a collection of information on RNA-protein interfaces based on data drawn from the PDB.
Some common features of protein-RNA interfaces were deduced based on known structures. For example, RNP in snRNPs have an RNA-binding
Structural motif in its RNA-binding protein.
Aromaticity amino acid residues in this motif result in stacking interactions with RNA.
Lysine residues in the
Helix portion of RNA-binding proteins help to stabilize interactions with nucleic acids. This nucleic acid binding is strengthened by
Electrostatics attraction between the positive lysine
and the negative
nucleic acid phosphate backbones. Additionally, it is possible to model RNPs computationally.
Although computational methods of deducing RNP structures are less accurate than experimental methods, they provide a rough model of the structure which allows for predictions of the identity of significant amino acids and nucleotide residues. Such information helps in understanding the overall function the RNP. proteins, stained white, hijack
active transport via the endosomes to move more rapidly within the cell than by simple
diffusion.
]]'RNP' can also refer to ribonucleoprotein particles. Ribonucleoprotein particles are distinct intracellular foci for post-transcriptional regulation. These particles play an important role in influenza A virus replication.
The influenza viral genome is composed of eight ribonucleoprotein particles formed by a complex of negative-sense RNA bound to a viral nucleoprotein. Each RNP carries with it an
RNA polymerase complex. When the nucleoprotein binds to the
Virus RNA, it is able to expose the nucleotide bases which allow the viral polymerase to transcribe RNA. At this point, once the virus enters a host cell it will be prepared to begin the process of replication.
Anti-RNP antibodies
Anti-RNP antibodies are
autoantibodies associated with
mixed connective tissue disease and are also detected in nearly 40% of Lupus erythematosus patients. Two types of anti-RNP antibodies are closely related to Sjögren's syndrome:
SS-A (Ro) and
SS-B (La).
Autoantibodies against
snRNP are called Anti-Smith antibodies and are specific for SLE. The presence of a significant level of anti-U1-RNP also serves a possible indicator of MCTD when detected in conjunction with several other factors.
Functions
The ribonucleoproteins play a role of protection.
never occur as free RNA molecules in the cell. They always associate with ribonucleoproteins and function as ribonucleoprotein complexes.
In the same way, the genomes of negative-strand RNA viruses never exist as free RNA molecule. The ribonucleoproteins protect their genomes from RNase.
See also
-
DNA-binding protein
-
RNA-binding protein
External links
