UBE2D4

UBE2D4 Full Name

ubiquitin-conjugating enzyme E2D 4 (putative)

UBE2D4 Introduction

Ubiquitin-conjugating enzyme E2D 4 (UBE2D4), also designated as putative UbcH5D or HBUCE1, is the most divergent and least characterized member of the UBE2D/UbcH5 family of E2 ubiquitin-conjugating enzymes. Encoded by the UBE2D4 gene on chromosome 7p13, UBE2D4 was identified through homology to the canonical UBE2D enzymes (UBE2D1, UBE2D2, UBE2D3) but exhibits significantly lower sequence identity (~70%) and key amino acid substitutions in regions critical for E3 ligase interaction and catalytic activity. Its designation as a putative E2 reflects the current uncertainty regarding its enzymatic competence and physiological substrates, and functional characterization of UBE2D4 remains incomplete relative to its well-studied paralogs.

Figure 1. Strcuture of UBE2D4.

Distinctive Structural Features and Uncertain Catalytic Activity
UBE2D4 contains the conserved ubiquitin-conjugating (UBC) domain fold characteristic of E2 enzymes, including the catalytic cysteine residue required for ubiquitin thioester bond formation. However, UBE2D4 diverges from UBE2D1-D3 at several key residues within the E3-binding interface and the ubiquitin-binding surface. In particular, amino acid substitutions in the N-terminal helix and in the loop regions flanking the catalytic site are predicted to alter the enzyme's ability to productively interact with the same spectrum of E3 ligases and to modulate its catalytic efficiency. Recombinant UBE2D4 can form a thioester with ubiquitin in vitro, confirming its biochemical capacity to function as an E2 enzyme, but its activity with specific E3 ligases and its ability to synthesize polyubiquitin chains remain poorly characterized. UBE2D4 is expressed at lower levels than other UBE2D family members in most tissues, with relatively higher expression detected in the testis. The gene encoding UBE2D4 is subject to imprinting in certain contexts, an unusual feature for an E2 enzyme that may contribute to its restricted expression pattern.

UBE2D4 in Imprinting Disorders, Spermatogenesis, and Emerging Disease Associations
UBE2D4 is located within a cluster of imprinted genes on chromosome 7p13 in a region syntenic with the mouse proximal chromosome 12 imprinted domain. Imprinted expression of UBE2D4 — with preferential expression from the paternal allele — has been documented, suggesting that UBE2D4 may be subject to parent-of-origin-specific gene regulation. This has potential relevance to imprinting disorders including Silver-Russell syndrome and Beckwith-Wiedemann syndrome, though direct evidence for UBE2D4 involvement remains to be established. The relatively high expression of UBE2D4 in the testis points to a possible role in spermatogenesis, where ubiquitin-mediated proteolysis is essential for the dramatic chromatin remodeling and protein turnover that accompanies sperm maturation. UBE2D4 has also been identified among differentially expressed genes in certain cancer transcriptomic studies, though whether its altered expression is causal or correlative is unknown. Comprehensive biochemical characterization, identification of cognate E3 partners, and determination of in vivo substrates represent priorities for advancing understanding of this enigmatic E2 enzyme.

Alternate Names for UBE2D4

UBE2D4; ubiquitin-conjugating enzyme E2D 4 (putative); ubiquitin-conjugating enzyme E2 D4; HBUCE1; ubiquitin-protein ligase D4; ubiquitin carrier protein D4; ubiquitin-conjugating enzyme HBUCE1; FLJ32004;

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