Adenoviruses (Ads) subvert MHC class I antigen presentation and impair host anti-Ad cellular activities. Specifically, the Ad-encoded E3-19K immunomodulatory protein targets MHC class I molecules for retention within the endoplasmic reticulum (ER) of infected cells. Here, we report the x-ray crystal structure of the Ad type 4 (Ad4) E3-19K of species E bound to HLA-A2 at 2.64 Å resolution. Structural analysis shows that Ad4 E3-19K adopts a tertiary fold that is shared only with Ad2 E3-19K of species C. A comparative analysis of the Ad4 E3-19K/HLA-A2 structure with our x-ray structure of Ad2 E3-19K/HLA-A2 identifies species-specific features in HLA-A2 recognition. Our analysis also reveals common binding characteristics that explain the promiscuous, and yet high-affinity, association of E3-19K proteins with HLA-A and -B molecules. We also provide structural insights into why E3-19K proteins do not associate with HLA-C molecules. Overall, our study provides new information into how E3-19K proteins selectively engage with MHC I to abrogate antigen presentation and counteract activation of CD8+ T-cells. The significance of MHC I antigen presentation for controlling viral infections, and the threats of viral infections in immunocompromised patients, underline our efforts to characterize viral immunoevasins such as E3-19K.