Research Article

Evolutionary Analysis of Post – translational Modification Sites in Translation Elongation Factor 1A

Yosuke Kondo, Satoru Miyazaki

  1. Department of Medicinal and Life Science, Faculty of Pharmaceutical Sciences, TokyoUniversity of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan

*Corresponding author: Satoru Miyazaki, Department of Medicinal and Life Science, Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan, Tel: +81-4-7121-3630; Fax: +81-4-7121-3630; E-mail:


Evolutionary conservation is one of the powerful analyses to predict protein functional sites. There have been many studies proposing a variety of degrees of conservation. In this paper, we propose and compare two mathematical measures that calculate the degree of conservation at each site in the molecular evolutionary process, named “the degree of conservation” and “the degree of specific conservation”. Thedegree of conservation can identify the sites which show a conserved pattern in all proteins of a proteinfamily. The degree of specific conservation is the degree that can identify the sites conserved in a subfamily but variable in the whole family. In this study, the conservation analyses were applied to a protein thathas many functions in the cell. Many researches of eukaryotic elongation factor 1A (eEF1A) revealed thateEF1A is involved in not only protein biosynthesis but also moonlighting functions such as cytoskeletalmodification, apoptosis and viral infection. And functional divergences of the EF-Tu/1A protein familyhave occurred in the evolutionary process. Our results showed that the degree of conservation can predictthe regions that are important for binding molecules of the eEF-Tu/1A proteins. The degree of specificconservation can predict the residues important for the functional divergences and post-translationalmodifications (PTMs). These results suggest that PTM sites of eEF1A are not conserved in the wholefamily but only conserved in a subfamily. It would be necessary to verify whether the conserved sitesare responsible for the moonlighting functions of eEF1A to develop new drugs that can be effective forcancers.

Keywords: evolutionary conservation, peptide elongation factor, post-translational modification


Eukaryotic translation elongation factor 1A (eEF1A) is an abundant protein in cells and delivers aminoacyl-tRNA onto a ribosome [1]. It is said that the principal function of eEF1A is protein biosynthesis. However,eEF1A is revealed as one of the multifunctional proteins [2]. Novel eEF1A functions such as cytoskeletalmodification, apoptosis, viral infection and so on [3] have been clarified from the discovery of the actinbinding function [4]. eEF1A is also identified as a protein attaching cell membranes to induce anoikisby inactivating β1-integrin [5]. The antiadhesive function from the extracellular matrix is effective todevelop new drugs for cancers such as leukemia [6].

In addition to the moonlighting functions, many functional divergences have been observed in theeEF1A family. There are two known isoforms of eEF1A proteins, eEF1A1 and eEF1A2, in which thesequences share 92% identity [7,8]. Expression of the gene coding eEF1A depends on cell types [9]; themajority of cells express eEF1A1, neuron or muscle cells often express eEF1A2 and some of other celltypes express both eEF1A isoforms. In order to elongate a polypeptide chain by eEF1As, GDP/GTPbinding is necessary. However, eEF1As do not have identical binding affinities with GDP and GTP [10];the GTP binding affinity of eEF1A1 is higher than eEF1A2 but that of eEF1A2 is higher than eEF1A1.

Furthermore, eEF1A1 promotes apoptosis [11] but overexpression of eEF1A2 causes cancers [12]. Suchfunctional differences are important for elucidating various cell functions.There are 36 non-identical residues between human eEF1A1 and eEF1A2. It is known that some ofthese residues or corresponding residues of eEF-Tu are estimated to be important for actin binding orfibronectin binding functional divergences [13, 14]. On the other hand, identical residues were estimatedto be also important for the functional divergences because GDP/GTP binding affinity is different becauseof non-identical residues that are close to the identical residues [15]. Recent studies showed that post-translational modification (PTM) sites of eEF1A determined by mass spectrometry analysis [16-18]are located on regions close to the non-identical residues [15]. PTM residues should be important foranalyzing the functional divergences of eEF1As.

PTM sites of eEF1A is previously estimated as non-conservation sites [19]. Meanwhile, our previousstudies showed that residues involving binding molecules or functional divergences of the EF-Tu/1Afamily can be predicted by evolutionary analysis [20, 21]. Therefore, evolutionary conservation of theEF-Tu/1A protein family is useful to investigate important residues of the proteins. In this paper, wepropose degrees of conservation and discuss what degree of conservation can accurately predict the PTMsites of eEF1A. This analysis would clarify how the PTM sites of eEF1A proteins are evolved.

Materials and Methods

Construction of the multiple sequence alignment and phylogenetic tree

From UniProtKB/Swiss-Prot [22], we collected 984 entries, which (1) are annotated as ‘Classic translationfactor GTPase family. EF-Tu/EF-1A subfamily’, (2) do not include ‘X’ in the sequence and (3) are not afragment. The sequences were aligned by MAFFT 7 program[23]. Distances of sequence pairs were com-puted by maximum likelihood method[24] using the Jones-Taylor-Thornton model[25] as a substitutionmatrix and the Dayhoff method[26] for computing equilibrium frequencies. From all combinations of thedistances, a phylogenetic tree was written by unweighted pair group method with arithmetic mean[27].

Preparation for defining degrees of conservation

Let M = (mij) denote a given multiple sequence alignment (MSA) and here mij denote an amino acidsymbol in sequence i of site j on the MSA. Let Xj = {m1j,m2j , . . . ,mnj} be a multiset of amino acidsymbols. Let Fjdenote a field of sets of Xj. And, let Fjtbe an element of Fj and a group by node t ina phylogenetic tree.

Mathematical formulation for a degree of variability

be a normalized substitution matrix, where Smax, Smin, S (y, y) and S (y, z) are the maximum, the minimum, a diagonal element and an off-diagonal element in an amino acid substitution matrix, respectively,and w (y) is a weight of sequence y. The Gonnet matrix [28] was used as a substitution matrix. Theweight was computed by Sibbald and Algos algorithm[29] and the iteration number was 100,000.

Mathematical formulation for degrees of conservation

Data collection of functional sites in eEF-Tu/1A

Binding residues were collected from three-dimensional structures of eEF-Tu/1A described in our previousstudy [21]. Actin-binding residues were obtained from site-directed mutagenesis data [30]. PTM siteswere obtained from the PhosphoSitePlus database [31].


Predicted sites by degrees of conservation

The multiple sequence alignment constructed from the sequences in the EF-Tu/1A family consisted of739 sites. The degrees of conservation and specific conservation were calculated at each site. In orderto determine a threshold of each degree of conservation, we used ROC (receiver operating characteristic)curves.

The ROC curve of the degree of conservation was created from proximity of binding molecules orions in three-dimensional structures of the EF-Tu/1A proteins as described in our previous paper [21].Because Figure 1A shows that the threshold is 0.973, predicted sites were defined as the sites in whichthe degree of conservation is higher or equal to the threshold. The predicted sites shown in Figure 1Bare mainly located on the left side of the three-dimensional structure.

The ROC curve of the degree of specific conservation was constructed from actin binding residues[13]. Because Figure 2A shows that the threshold is 0.190, predicted sites were defined as the sites inwhich the degree of specific conservation is higher or equal to the threshold. The predicted sites shownin Figure 2B are mainly located on the right side of the three-dimensional structure.

In order to clarify the difference of the predicted sites between each degree of conservation, we investigated overlapping predicted residues shown in Figure 3A. Hundred residues were overlapping residuesthat were predicted both degrees of conservation. Figure 3B also shows that the degrees of conservationand specific conservation mainly predicted the left and right side of the three-dimensional structure, respectively.

The degrees of conservation and PTM sites

PTM sites of eEF1A1 in human, mouse, rat and rabbit and eEF1A2 in human, mouse and rat were shownin Figure 4. In order to analyze which degree of conservation can accurately predict the PTM sites, thetrue positive rate and the false positive rate were calculated as shown in Table 1. The true positive rateof the degree of specific conservation is 0.827. This value is higher than that of the degree of conservation.

Meanwhile, the false positive rate of the degree of specific conservation is higher that of the degree of conservation. In addition, we created ROC curves of PTM sites and each degrees of conservation showning Figure 5. The AUC (0.773) of the degree of specific conservation is higher than the AUC (0.649) ofthe degree of conservation.


In this paper, we investigated the conserved sites of eEF1A using two degrees of conservation. One isthe degree that can identify the sites which show a conserved pattern in all proteins of a protein family.As shown in our previous study [21], the degree of conservation can predict close sites from bindingmolecules in the three-dimensional structures of eEF-Tu/1A. eEF1A has the conserved face and thevariable face in the three-dimensional structure [15]. These faces were decided from variable residuesbetween eEF1A1 and eEF1A2. The conserved face is similar to the regions that are determined by thedegree of conservation shown in Figure 1B. This shows that the degree of conservation can predict theconserved face of eEF1A.

The other degree of conservation is a specific conservation that can identify the sites that are onlyconserved in a subfamily of a protein family. In other words, the degree of specific conservation canidentify the sites conserved in the subfamily but variable in the whole family. In this study, the subfamilyis specified as the group that contains vertebrate eEF1A1 and eEF1A2. The whole family is specified asthe group that contains whole eEF-Tu/1A family. Therefore, the degree of specific conservation predictsfew non-identical sites between eEF1A1 and eEF1A2. However, the degree of specific conservation canmainly predict close sites from the non-identical residues shown in Figure 2. This suggests that the degreeof specific conservation can predict the residues that are important for functional divergences betweeneEF1A1 and eEF1A2. In addition, the regions that are predicted from the degree of specific conservationare similar to the variable face described above. Because there are many PTM sites in the variable face,the specific conservation may be useful for predicting PTM sites.

As shown in Table 1 and Figure 5, our results show that the PTM sites were predicted well by thedegree of specific conservation than degree of conservation. In addition, Table 1 shows that the truepositive rate is high but the false positive rate is high in the degree of specific conservation. Therefore,the degree of specific conservation can accurately predict the known PTM sites that are registered inthe database of PTM sites. This shows that the degree of specific conservation is superior to the degree of conservation to predict PTM sites of eEF1A proteins. These results suggest that one degree ofconservation is inadequate to predict all important residues of eEF1A.

In conclusion, various degrees of conservation may be useful when we predict functional sites ofmultifunctional proteins like eEF1A proteins. In addition, our results suggest that PTM sites of eEF1A1and eEF1A2 are not conserved in the whole family but conserved in the subfamily.


eEF: eukaryotic elongation factor; MSA: multiple sequence alignment; PTM: post-translational modification

Conflict of Interest

The authors declare no conflict of interest.

Table 1. Accuracy for predicting PTM sites by degree of conservation or specific conservation.

True positive rate False positive rate
C_ 0.395 0.291 C_ 0.827 0.376


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Received:  July 18, 2018;
Accepted: August 17, 2018;
Published: August 21, 2018

To cite this article:

Kondo Y, Miyazaki S. Evolutionary Analysis of Post-translational Modification Sites in Translation Elongation Factor 1A. Japan Journal of Medicine. 2018: 1:6.

©Kondo Y, et al. 2018.