ULBP3

ULBP3 Full Name

UL16 binding protein 3

ULBP3 Introduction

ULBP3 encodes UL16-binding protein 3, a cell-surface glycoprotein that functions as a ligand for the activating immune receptor NKG2D. Although ULBP3 is structurally related to classical major histocompatibility complex (MHC) class I molecules, it is not encoded within the MHC locus; instead, its gene resides in a cluster of related genes on chromosome 6. Unlike conventional MHC class I proteins, ULBP3 lacks the α3 domain and the transmembrane segment, consisting instead of an α1α2 ectodomain that is tethered to the outer leaflet of the plasma membrane by a glycosylphosphatidylinositol anchor. This MHC class I-like but non-classical architecture is shared across the ULBP family and underlies their role as immunological alarms rather than peptide presenters. ULBP3 is one of several ULBP family members that serve as stress-induced signals recognized by immune cells.

Figure 1. NKG2D ligand (NKG2DL) binding activates the cytotoxic potential of effector cells. (Source: Jones AB, et al. 2022)

The physiological role of ULBP3 is to alert the immune system to cells under stress. When ULBP3 engages NKG2D on natural killer cells and certain T cells, it delivers a potent activating signal that can trigger release of cytotoxic granules and target-cell killing. Normal tissues generally keep ULBP3 expression low, but its surface levels rise in response to malignant transformation, DNA damage, or viral infection — conditions that make a cell a candidate for immune elimination. The importance of this axis is highlighted by cytomegalovirus, which encodes the glycoprotein UL16 to bind and sequester ULBP proteins away from NKG2D, thereby helping infected cells evade detection. Structural work has revealed how the NKG2D receptor docks onto the ULBP3 ectodomain, explaining the molecular basis of recognition. Because ULBP3 can be exploited therapeutically — either by boosting its expression on tumors or by blocking it in autoimmune settings — it has become a focus of immunotherapy research, positioning it as a central component of innate immune surveillance that translates cellular distress into an actionable immune signal.

Alternate Names for ULBP3

ULBP3; UL16 binding protein 3; NKG2D ligand 3; RAET1N; ALCAN- gamma; N2DL-3; N2DL3; NKG2D ligand 3; NKG2D ligand 3 precursor; NKG2DL3; OTTHUMP00000017411; RAET1N; Retinoic acid early transcript 1N; UL16 binding protein 3; UL16-binding protein 3; N2DL-3; N

• 1. Jones AB, et al. Regulation of NKG2D Stress Ligands and Its Relevance in Cancer Progression. Cancers (Basel). 2022 May 9;14(9):2339.
  2. Radaev S, et al. Conformational plasticity revealed by the cocrystal structure of NKG2D and its class I MHC-like ligand ULBP3. Immunity. 2001 Dec;15(6):1039-49.