Invariant chain transmembrane domain trimerization: a step in MHC class II assembly.
The transmembrane (TM) domain of the major histocompatibility complex (MHC) class II-associated invariant chain (Ii) has long been implicated in both correct folding and function of the MHC class II complex. To function correctly, Ii must form a trimer, and the TM domain is one of the domains thought to stabilize the trimeric state. Specific mutations in the TM domain have been shown previously to disrupt MHC class II functions such as mature complex formation and antigen presentation, possibly due to disruption of Ii TM helix-helix interactions. Although this hypothesis has been reported several times in the literature, thus far no experimental measurements have been made to explore the relationship between TM domain structure and TM mutations that affect Ii function. We have applied biophysical and computational methods to study the folding and assembly of the Ii TM domain in isolation and find that the TM domain strongly self-associates. According to analytical ultracentrifugation analyses, the primary oligomeric state for this TM domain is a strongly associated trimer with a dissociation constant of approximately 120 nM in DPC micelles. We have also examined the effect of functionally important mutations of glutamine and threonine residues in the TM domain on its structure, providing results that now link the disruption of TM helix interactions to previously reported losses of Ii function.
Dixon
Ann M
AM
Department of Molecular Biophysics and Biochemistry, Yale University, P.O. Box 208114, New Haven, Connecticut 06510, USA.
Stanley
Bradford J
BJ
Matthews
Erin E
EE
Dawson
Jessica P
JP
Engelman
Donald M
DM
D000595:Amino Acid Sequence; D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D000944:Antigens, Differentiation, B-Lymphocyte; D003902:Detergents; D000949:Histocompatibility Antigens Class II; C045084:invariant chain