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Structural highlights of the METTL3/METTL14 complex

[1]

Primary structure This complex is composed of two differents proteins forming two distinct but linked subunit of the enzymatic complex/. Each of these two protein is coded by two differents genes. The mettl3 gene codes for the N6-adenosine-methyltransferase 70 kDa subunit, which is a 225 Amino acid chain, whereas the Mettl14 codes for the N6-adenosine-methyltransferase subunit METTL14, which is composed of 349 amino acids.

Each of these two proteins are corresponding to the A [2]or the B chain [3] of the complex.

Secondary structure

Both polypeptides METTL3 and METTL14 are able to form some secondary structure thank interchain and intrachain hydrogen bond formation.

Chain A METTL3'secondary structure, is mainly composed of 20% helical (7 helices; 46 residues)and 24% beta sheet (13 strands; 55 residues)

              [3]

Chain B METTL14 is made of 24% helical s (14 helices; 87 residues) and 18% beta sheet (16 strands; 63 residues)

Tertiary structure

Domains and specific site or sequences

Thanks to their primary amino acid sequences both A and B chains have some specific conserved domains directly linked to their function and functionning.

METTL3 and MTTL14 have both a methyltranferase domain but the complex METTL3/METTL14 has a better methyltransferase activity. Moreover, a mutatio in the catalytic center of METTL3 inhibits the hole methyltransferase activity of the complex, whereas a mutation in the catalytic center of METTL14 does not. Thus, METTL3 is the catalytic subunit of the complex and METTL14 enhances the methyltransfearse activity by stabilizing the complex and enables the recognition of consensus sequence on messenger RNA.

Cristal structure

To study the crital structure of the METTL3/METTL14 some cristalograghy experiments have been realizes under the following experimental conditions to cristalyze the protein complex:

Method : Vapor Diffusion Hanging Drop

pH 8

Temperature : 291.0 K

Buffer: 0.1 M Tris pH 8.0, 20% PEG3350

After critalization, cristal had been analyzed through X-Ray diffraction, at 100°C, with a single wavelength coming out of a synchrotron.

Thanks to the experiment the following data have been collected to describe the cristal structure of the complex :

Unit Cell caracteristics :

Length (Å) a = 101.86 b = 101.86 c = 117.66

Angle (°) α = 90 β = 90 γ = 90

Symmetry :

Space Group P 41 21 2

The primitive cubic symmetry of the unit cell is driven by two 2-fold axis rotation. Moreover, within this space group which is acentric, chiral, and enantiomorphic with one single lattice translations, eight different representative symmetry operations are needed to get the whole unit cell.

The cristal structure analysis at 1,65 angstrom allow to collect precise and detailled informations about the whole structure like the side chains and also the hydrogen bonds. (Cristal analysis data at other resolution are available on [4].)

Complex METTL3/METTL14 enzymatic working process

The enzymatic complex of two proteins is abble to realize methylation reactions thanks to its sequence and specific which allow it to catalyze some perticular reactions at given sites.

The complex METTL3/METTL14 belongs to the writers group, which means that theses two proteins are taking part to the protein subunit able to realize the post transcriptional modification of the RNA within the humans cells.

The METTL3/METTL14 complex catalyze the methylation reaction.

Function of the modification within the cell

Specific, and well controlled methylation of the nucleic acids is essential for proper gene regulation, whatever the studied organism or modification’s type. However the precise molecular role of m6A is unknown, it is knonw that for most mRNAs, m6A modification appear in long exons, near stop codons, and in 3′ UTRs and that this modification could influence mRNA stability, induce RNA conformational changes, modulate protein-RNA interactions, and even modify microRNA processing One of the most prevalent modifications observed for mRNAs is N6-methyladenosine (m6A). Recent studies have intensely investigated how m6A-modification of RNA contributes to central events in biology. Nonfonctional m6A actors such as writers like METTL3 or METTL14, but also readers, and erasers are oftern linked to problems in self-renewal of stem cells, circadian clock and developmental defects, obesity, synaptic signaling, and cancers.

Disease and problems triggered by unfunctionnal METTL3/METTL14 complex

Relevance

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