Sequence specificity in the dimerization of transmembrane .alpha.-helixes

Abstract

While several reports have suggested a role for helix-helix interactions in membrane protein oligomerization, there are few direct biochemical data bearing on this subject. Here, using mutational analysis, we show that dimerization of the transmembrane alpha-helix of glycophorin A in a detergent environment is spontaneous and highly specific. Very subtle changes in the side-chain structure at certain sensitive positions disrupt the helix-helix association. These sensitive positions occur at approximately every 3.9 residues along the helix, consistent with their comprising the interface of a closely fit transmembranous supercoil of alpha-helices. By contrast with other reported cases of interactions between transmembrane helices, the set of interfacial residues in this case contains no highly polar groups. Amino acids with aliphatic side chains define much of the interface, indicating that precise packing interactions between the helices may provide much of the energy for association. These data highlight the potential general importance of specific interactions between the hydrophobic anchors of integral membrane proteins.

Comparative Characterization of a Wild Type and Transmembrane Domain-Deleted Fatty Acid Amide Hydrolase: Identification of the Transmembrane Domain as a Site for Oligomerization

“…The ability of transmembrane domains to form specific, and often SDS-resistant, homo-oligomeric structures has been demonstrated for a small but growing family of proteins (51). The most well studied example of a protein that forms transmembrane domain-mediated homodimers is glycophorin A, whose transmembrane domain, like that of FAAH, is sufficient to induce dimerization in the context of a heterologous fusion protein (52). Interestingly, recent structural information on a dimer of the glycophorin A transmembrane domain has shown that van der Waals interactions alone suffice to generate stable and specific molecular self-association (53).…”

Transmembrane Domain Interactions Control Biological Functions of Neuropilin-1

“…Its dimerization is due to strong interactions between the TM domains of two monomers. Mutagenesis studies have defined the amino acid motif involved in the interactions (Lemmon et al, 1992), and a reporter gene dimerization assay (TOXCAT) has confirmed this motif (Russ and Engelman, 1999). The interaction has also been quantified by FRET (Fisher et al, 1999).…”

The dimerization interface of the glycoprotein Ibβ transmembrane domain corresponds to polar residues within a leucine zipper motif

“…SDS-PAGE provides a simple, direct, and quick method to detect mutational effects on the TM-TM association. 10,17,21 As shown in Figure 4(A), the wild-type Ibb TM peptide (termed ''Ibb TMpep'') and three Ibb mutant TM peptides, mutation of Ala128 to Leu (IbbA128L TMpep), mutation of Gly136 to Leu (IbbG136L TMpep), and mutation of His139 to Leu (IbbH139L TMpep), were expressed in E. coli and purified by HPLC. Mutation of Gln129 to Leu (IbbQ129L TMpep) was not included Figure 3.…”

“…10 Sequence-specific association between a-helical TM domains supports the proper assembly of many integral membrane proteins. Biochemical and functional analyses, molecular modeling, and structural studies have indicated that the association of TM helices is driven by a close packing of their characteristically shaped surfaces.…”