A Highly Conserved Phenylalanine in the α, β‐T Cell Receptor (TCR) Constant Region Determines the Integrity of TCR/CD3 Complexes

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Abstract
In the present study, we have investigated the importance of a phenylalanine (phe195) in the Tcr‐Cα region on Tcr‐α, β/CD3 membrane expression. An exchange of phe195 with a tyrosine residue does not affect Tcr/CD3 membrane expression; however, exchange with aspartic acid, histidine or valine prohibit completely Tcr/CD3 membrane expression. This seems to be due to a lack of interaction between mutated Tcr‐α, β/CD3‐γɛ, δɛ complexes and ζ2 homodimers. The Tcr‐Cα region around phe195 seems together with the same region in the Tcr‐Cβ region to constitute an interaction site for ζ2 homodimers. The presence of phe195 on both Tcr‐Cα and Tcr‐Cβ causes high avidity interaction with ζ2 homodimers, whereas his195 in both Tcr‐Cγ and Tcr‐Cδ results in an apparently lower avidity interaction with ζ2 homodimers. It is suggested that the phe195 region (on β‐strand F) and eventually adjacent aromatic amino acid residues on β‐strand B region may play an important role in Tcr‐α, β/CD3 membrane expression, in Tcr‐α, β/CD3 competition with Tcr‐γ, δ/CD3 complexes for ζ2 homodimers and in the control of formation of ‘mixed’ Tcr heterodimers.