*2.3. Amino Acid Composition and Amino Acid Sequence of OM Porin from M. primoryensis KMM 3633<sup>T</sup>*

*M. primoryensis* KMM 3633<sup>T</sup> whole genome was sequenced, assembled, and annotated as described in Methods. The porin of *M. primoryensis* KMM 3633<sup>T</sup> was classified as Porin\_4 according to the conservative domain searching and analyzed in detail. The characteristics are represented in Table 1. By protein BLAST we revealed proteins with high sequences similarity and proteins with similar domain architecture. Porins of *M. primoryensis* strain AceL and *Marinomonas* sp. strain IMCC 4694 had the highest similarity with porin of strain KMM 3633T-83.59% and 77.43%, respectively. Porins of *Polaromonas sp*. JS666, *Magnetospirillum magneticum* AMB-1 and *Basfia succiniciproducens* MBEL55E had the most closely related domain architecture with analyzed porin. Porins of *Photobacterium damselae* [27] and *Escherichia coli* [28] were chosen as well-known porins: the first one is from marine Gammaproteobacteria, the fish pathogen, and the second one is from terrestrial Gammaproteobacteria, the classical object of biological and molecular research. Amino acid composition of the isolated proteins [27,28] was supplemented by translation of sequenced genes.

Most of the bacteria represented in Table 1 are aquatic, isolated from sea-, ground-, or bog water. *E. coli* and *B. succiniciproducens* are known as habitants of gastrointestinal tract (GIT). All eight analyzed bacteria were Proteobacteria, six of them were from class Gammaproteobacteria. According to the Pmaf classification porins of aquatic bacteria belong to one superfamily, and GIT bacteria—to another. According to TBCD (Transporter Classification DataBase) all porins belonged to the same superfamily and all but one were assigned to the same family. As follows from the data shown in Table 2, eight porins were not much different in number of amino acids, protein molecular weight, and aliphatic index, but significant differences were revealed in theoretical pI, total number of negatively and positively charged residues, and differences in the content of tryptophan residues. This amino acid was absent in the porins of the three *Marinomonas* sp. strains and *Photobacterium damselae subsp. damselae* and was in low amount in porin of *Polaromonas* sp. JS666 in comparison with porins of the GIT bacteria. All porins analyzed are enriched in polar amino acids and have a significantly higher level of acidic amino acids (15.9–28.8 mol %) compared with the basic amino acids (5.1–16.4 mol %), that is typical for classical gram-negative porins. Despite noted differences all porins had close polarity values calculated by two methods.

The polarity of MpOmp was 44.25 (from amino acid composition) and 50.7 (from DNA translation) calculated as reported previously [29]. The polarity index of the protein studied was 1.81 (from amino acid composition) and 1.95 (from DNA translation) calculated by [30]. The value is close to the average that of similar values for other proteins belonging to the Protein\_4 superfamily represented in Table 1. This result and GRAVY index (Table 1) indicate that porin from *M. primoryensis* KMM 3633<sup>T</sup> is relatively hydrophilic protein.

ProtParam tool allows the computation of the instability index on the base of dipeptide composition. Since the proteins with instability index value below 40 are stable proteins [31], all porins from our analysis are stable, and porins of *M. primoryensis* KMM 3633T and *M. primoryensis* AceL was predicted to be the most stable (Table 1).


Comparison of porin characteristics of some Proteobacteria.

**Table**

**1.**

#### *Molecules* **2020** , *25*, 3131


Proteobacteriaporins.

#### *Molecules* **2020**, *25*, 3131
