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H R Turnquist

Publications and source records attributed to H R Turnquist.

6 recordsLinked to original sources
PubMed2002

Calreticulin binds to the alpha1 domain of MHC class I independently of tapasin.

Prior to binding to antigenic peptide, the major histocompatibility complex (MHC) heavy chain associates with an assembly complex of proteins that includes calreticulin, tapasin, and the transporter associated with antigen processing (TAP). Our data show that calreticulin can bind weakly to Ld without tapasin's assistance, and that deglycosylation of the alpha1 domain results in a primary loss of binding to calreticulin rather than tapasin. We have also shown that high amounts of wild-type tapasin are still unable to associate with MHC class I in the absence of the MHC class I/calreticulin interaction, confirming the central role of calreticulin in the formation of the MHC class I assembly complex.

ATP-Binding Cassette Transporters↗
PubMed2001

Loss of a glycine in the alpha2 domain affects MHC peptide binding but not chaperone binding.

Prior to the binding of peptide in the endoplasmic reticulum (ER), the major histocompatibility complex (MHC) class I heavy chain associates with an assembly complex that includes the transporter associated with antigen processing (TAP). The proximity of a part of the MHC class I alpha2 domain alpha-helix to areas previously shown to influence assembly complex binding suggests that this region might also be involved in chaperone association. Position 151, found in this part of the alpha2 domain alpha-helix, has a side chain that points up, away from direct contact with peptide, and is occupied by a glycine in all murine MHC class I heavy chains. We found that substitution of this glycine in H-2L(d) with a histidine substantially increased the proportion of peptide-free forms, although TAP binding was not abrogated. Thus, interaction of the heavy chain with peptides, but not with the assembly complex, is influenced by this glycine.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

A region of tapasin that affects L(d) binding and assembly.

Tapasin has been shown to stabilize TAP and to link TAP to the MHC class I H chain. Evidence also has been presented that tapasin influences the loading of peptides onto MHC class I. To explore the relationship between the ability of tapasin to bind to TAP and the MHC class I H chain and the ability of tapasin to facilitate class I assembly, we have created novel tapasin mutants and expressed them in 721.220-L(d) cells. One mutant has a deletion of nine amino acid residues (tapasin Delta334-342), and the other has amino acid substitutions at positions 334 and 335. In this report we describe the ability of these mutants to interact with L(d) and their effects on L(d) surface expression. We found that tapasin Delta334-342 was unable to bind to the L(d) H chain, and yet it facilitated L(d) assembly and expression. Tapasin Delta334-342 was able to bind and stabilize TAP, suggesting that TAP stabilization may be important to the assembly of L(d). Tapasin mutant H334F/H335Y, unlike tapasin Delta334-342, bound to L(d). Expression of tapasin H334F/H335Y in 721.220-L(d) reduced the proportion of cell surface open forms of L(d) and retarded the migration of L(d) from the endoplasmic reticulum. In total, our results indicate that the 334-342 region of tapasin influences L(d) assembly and transport.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

HLA-B polymorphism affects interactions with multiple endoplasmic reticulum proteins.

To explore the nature of amino acid substitutions that influence association with TAP, we compared a site-directed mutant of HLA-B*0702 (Y116D) to unmutated HLA-B7 in regard to TAP interaction. We found that the mutant had stronger association with TAP, and, in addition, with tapasin and calreticulin. These data confirm the importance of position 116 for TAP association, and indicate that (1) an aspartic acid at the 116 position can facilitate the interaction, and (2) association with tapasin and calreticulin is affected along with TAP. Furthermore, we tested three natural subtypes of HLA-B15, and found that a B15 subtype with a tyrosine at position 116 (B*1510) was strongly associated not only with TAP, but also with tapasin and calreticulin. In contrast, two B15 subtypes with a serine at position 116 (B*1518 and B*1501) exhibited very little or no association with any of these proteins. Thus, very closely related HLA-B subtypes can differ in regard to interaction with the entire assembly complex. Interestingly, when their surface expression was tested by flow cytometry, the HLA-B15 subtypes with little to no detectable intracellular assembly complex association had a slightly, yet consistently, higher level of the open heavy chain form than did the B15 subtype with intracellular assembly complex association. These data suggest that the relatively low strength or short length of interaction between endoplasmic reticulum proteins and natural HLA class I molecules can decrease their surface stability.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

An extensive region of an MHC class I alpha 2 domain loop influences interaction with the assembly complex.

Presentation of antigenic peptides to CTLs at the cell surface first requires assembly of MHC class I with peptide and beta 2-microglobulin in the endoplasmic reticulum. This process involves an assembly complex of several proteins, including TAP, tapasin, and calreticulin, all of which associate specifically with the beta 2-microglobulin-assembled, open form of the class I heavy chain. To better comprehend at a molecular level the regulation of class I assembly, we have assessed the influence of multiple individual amino acid substitutions in the MHC class I alpha 2 domain on interaction with TAP, tapasin, and calreticulin. In this report, we present evidence indicating that many residues surrounding position 134 in H-2Ld influence interaction with assembly complex components. Most mutations decreased association, but one (LdK131D) strongly increased it. The Ld mutants, with the exception of LdK131D, exhibited characteristics suggesting suboptimal intracellular peptide loading, similar to the phenotype of Ld expressed in a tapasin-deficient cell line. Notably, K131D was less peptide inducible than wild-type Ld, which is consistent with its unusually strong association with the endoplasmic reticulum assembly complex.

ATP Binding Cassette Transporter, Subfamily B, Mem↗