Abstract
Avian influenza virus cross-species infection in humans poses a major threat to global public health. Species-specific differences between avian ANP32A and mammalian ANP32 proteins create a natural barrier against viral cross-species infection by directly impairing the functional interaction between the avian-origin viral RNA polymerase and mammalian ANP32 proteins, thereby restricting viral genome replication. The key to overcoming this barrier lies in the adaptation of viral RNA polymerase to host ANP32 family proteins. This mini-review summarizes the mechanisms and variations in influenza virus adaptation to ANP32 proteins across different species. Influenza viruses adapt to species-specific ANP32 proteins through various mutations and display distinct preferences for specific ANP32 family members within the same host. Additionally, alternative splicing variants of ANP32A within a single species further modulate viral RNA polymerase adaptability. Despite this diversity, the underlying interaction mechanism remains conserved: ANP32-polymerase binding is necessary but not sufficient for optimal polymerase activity. This interaction facilitates the formation of asymmetric polymerase dimers and specifically supports viral genome replication, while the step from cRNA to vRNA remains subject to species-specific restrictions. This explains the classic adaptive mechanism of the PB2 E627K mutation, which restores efficient viral genome replication through acid-base pairing with ANP32A. Furthermore, adaptive mutations in emerging strains such as H3N2 canine influenza virus and recent cases of H5N1 in dairy cows underscore the need for continuous viral surveillance and deeper mechanistic studies on virus-ANP32 interactions. Such research is strategically critical for advancing the One Health approach and mitigating future influenza pandemics.