Acromegaly in Carney complex

PURPOSE

Carney complex (CNC) is a rare autosomal dominant syndrome, characterized by mucocutaneous pigmentation, cardiac, cutaneous myxomas and endocrine overactivity. It is generally caused by inactivating mutations in the PRKAR1A (protein kinase cAMP-dependent type I regulatory subunit alpha) gene. Acromegaly is an infrequent manifestation of CNC, reportedly diagnosed in 10% of patients.

METHODS

We here report the case of a patient who was concomitantly diagnosed with Carney complex, due to a new mutation in PRKAR1A ((NM_002734.3:c.80_83del, p.(Ile27Lysfs*101 in exon 2), and acromegaly. In parallel, we conducted an extensive review of published case reports of acromegaly in the setting of CNC.

RESULTS

The 43-year-old patient was diagnosed with an acromegaly due to a GH-secreting pituitary microadenoma resistant to somatostatin analogs. He underwent transsphenoidal surgery in our tertiary referral center, which found a pure GH-secreting adenoma. In the literature, we identified 57 cases (24 men, 33 women) of acromegaly in CNC patients. The median age at diagnosis was 28.8 ± 12 year and there were 6 cases of gigantism. Acromegaly revealed CNC in only 4 patients. 24 patients had a microadenoma and two carried pituitary hyperplasia and/or multiple adenomas, suggesting that CNC may result in a higher proportion of microadenoma as compared to non-CNC acromegaly.

CONCLUSIONS

Although it rarely reveals CNC, acromegaly is diagnosed at a younger age in this setting, with a higher proportion of microadenomas.

Structural basis for the recognition of C20:2-αGalCer by the invariant natural killer T cell receptor-like antibody L363

Natural killer T (NKT) cells express a semi-invariant Vα14 T cell receptor (TCR) and recognize structurally diverse antigens presented by the antigen-presenting molecule CD1d that range from phosphoglycerolipids to α- and β-anomeric glycosphingolipids, as well as microbial α-glycosyl diacylglycerolipids. Recently developed antibodies that are specific for the complex of the prototypical invariant NKT (iNKT) cell antigen αGalCer (KRN7000) bound to mouse CD1d have become valuable tools in elucidating the mechanism of antigen loading and presentation. Here, we report the 3.1 Å resolution crystal structure of the Fab of one of these antibodies, L363, bound to mCD1d complexed with the αGalCer analog C20:2, revealing that L363 is an iNKT TCR-like antibody that binds CD1d-presented αGalCer in a manner similar to the TCR. The structure reveals that L363 depends on both the L and H chains for binding to the glycolipid-mCD1d complex, although only the L chain is involved in contacts with the glycolipid antigen. The H chain of L363 features residue Trp-104, which mimics the TCR CDR3α residue Leu-99, which is crucial for CD1d binding. We characterized the antigen-specificity of L363 toward several different glycolipids, demonstrating that whereas the TCR can induce structural changes in both antigen and CD1d to recognize disparate lipid antigens, the antibody L363 can only induce the F' roof formation in CD1d but fails to reorient the glycolipid headgroup necessary for binding. In summary, L363 is a powerful tool to study mechanism of iNKT cell activation for structural analogs of KRN7000, and our study can aid in the design of antibodies with altered antigen specificity.

Crystal structure of bovine CD1b3 with endogenously bound ligands

The CD1 family of Ag-presenting molecules is able to display lipids to T cells by binding them within a hydrophobic groove connected to the protein surface. In particular, the CD1b isotype is capable of binding ligands with greatly varying alkyl chain lengths through a complex network of interconnected hydrophobic pockets. Interestingly, mycobacterial lipids such as glucose monomycolate exclusively bind to CD1b. We determined the crystal structure of one of the three expressed bovine CD1b proteins, CD1b3, in complex with endogenous ligands, identified by mass spectrometry as a mixture of phosphatidylcholine and phosphatidylethanolamine, and analyzed the ability of the protein to bind glycolipids in vitro. The structure reveals a complex binding groove architecture, similar to the human ortholog but with consequential differences. Intriguingly, in bovine CD1b3 only the A', C' and F' pockets are present, whereas the T' pocket previously described in human CD1b is closed. This different pocket conformation could affect the ability of boCD1b3 to recognize lipids with long acyl chains such as glucose monomycolate. However, even in the absence of a T' tunnel, bovine CD1b3 is able to bind mycolates from Rhodococcus ruber in vitro.

NMR assignment of the periplasmic oxidoreductase DsbH from Chlamydia

Chlamydia use a complex of outer envelope proteins, which are highly cross-linked by disulfide bonds, to protect their infectious developmental form from lysis. Reported herein are the NMR chemical shift assignments of DsbH, a novel disulfide oxidoreductase from Chlamydia.

High yield expression and purification of isotopically labelled human endothelin-1 for use in NMR studies

Human endothelin-1 (ET-1) is a potent vasocontractile 21-residue peptide hormone with significant pharmacological importance. An efficient and straightforward expression strategy that enables cost-effective incorporation of stable isotopes is not available thus far. In this report, we describe a cost-effective expression system in Escherichia coli for the production of ET-1 enriched with (15)N and (13)C isotopes. Employing thioredoxin as carrier protein, specific and nearly quantitative cleavage of ET-1 from the fusion was mediated by Factor Xa, and purification to homogeneity (final purity of >95%) was achieved by RP-HPLC. Purified recombinant ET-1 was found to be indistinguishable from the synthetic counterpart as determined by mass spectrometry and NMR spectroscopy. Our expression strategy offers the potential for production of isotopically labeled ET-1 in large (mg) quantities for the purpose of heteronuclear NMR experiments. Moreover, the method devised should be applicable for recombinant expression of small peptides in general.