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[摘要]：Integrins are heterodimeric (alpha and beta subunits) signal transducer proteins involved in cell adhesions and migrations. The cytosolic tails of integrins are essential for transmitting bidirectional signaling and also implicated in maintaining the resting states of the receptors. In addition, cytosolic tails of integrins often undergo post-translation modifications like phosphorylation. However, the consequences of phosphorylation on the structures and interactions are not clear. The leukocyte-specific integrin alpha M beta 2 is essential for myeloid cell adhesion, phagocytosis, and degranulation. In this work, we determined solution structures of the myristoylated cytosolic tail of alpha M and a Ser phosphorylated variant in dodecylphosphocholine micelles by NMR spectroscopy. Furthermore, the interactions between non-phosphorylated and phosphorylated alpha M tails with beta 2 tail were investigated by NMR and fluorescence resonance energy transfer (FRET). The three-dimensional structures of the 24-residue cytosolic tail of alpha M or phosphorylated alpha M are characterized by an N-terminal amphipathic helix and a loop at the C terminus. The residues at the loop are involved in packing interactions with the hydrophobic face of the helix. (15)N-(1)H heteronuclear single quantum coherence experiments identified residues of alpha M and beta 2 tails that may be involved in the formation of a tail-tail heterocomplex. We further examined interactions between myristoylated beta 2 tail in dodecylphosphocholine micelles with dansylated alpha M tail peptides by FRET. These studies revealed enhanced interactions between alpha M or phosphorylated alpha M tails with beta(2) tail with K(d) values similar to 5.2 +/- 0.6 and similar to 4.4 +/- 0.7 mu M, respectively. Docked structures of tail-tail complexes delineated that the alpha M/beta 2 interface at the cytosolic region could be sustained by a network of polar interactions, ionic interactions, and/or hydrogen bonds. |
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