The regulatory role of the kinase-homology domain in receptor guanylyl cyclases: nothing ‘pseudo’ about it!

Abstract

The availability of genome sequence information and a large number of protein structures has allowed the cataloging of genes into various families, based on their function and predicted biochemical activity. Intriguingly, a number of proteins harbor changes in the amino acid sequence at residues, that from structural elucidation, are critical for catalytic activity. Such proteins have been categorized as ‘pseudoenzymes’. Here, we review the role of the pseudokinase (or kinase-homology) domain in receptor guanylyl cyclases. These are multidomain single-pass, transmembrane proteins harboring an extracellular ligand-binding domain, and an intracellular domain composed of a kinase-homology domain that regulates the activity of the associated guanylyl cyclase domain. Mutations that lie in the kinase-homology domain of these receptors are associated with human disease, and either abolish or enhance cGMP production by these receptors to alter downstream signaling events. This raises the interesting possibility that one could identify molecules that bind to the pseudokinase domain and regulate the activities of these receptors, in order to alleviate symptoms in patients harboring these mutations.

The pseudokinase domains of guanylyl cyclase–A and –B allosterically increase the affinity of their catalytic domains for substrate

“…ATP also stimulates the heat-stable enterotoxin receptor, GC-C, and the retinal GC, GC-E. Both of these receptors contain PKDs that lack the catalytic base but retain the invariant lysine (Lys 535 in GC-A) and the Mg 2+ -chelating aspartate (Asp 646 in GC-A) and are known to be activated by ATP in GC assays mimicking physiologic conditions (32,43,60,61). Furthermore, both the entire R-spine and the C-lobe portion of the C-spine are conserved in GC-C and GC-E. Substrate-velocity assays for GC-C revealed that the V max of the enzyme increased under both basal and peptide-stimulated conditions with the addition of ATP--S, with no change in K m as observed with GC-A and GC-B (62).…”

Impaired Intestinal Sodium Transport in Inflammatory Bowel Disease: From the Passenger to the Driver's Seat

“…The kinase homology domain (KHD) or the pseudo-kinase domain of GC-C plays an important role in ligand-mediated receptor activation and cGMP production [26,30,36]. We have previously shown that KHD in GC-C has a functional ATP-binding site and ATP binding triggers a conformational change, resulting in allosteric modulation of the receptor activity [37].…”

Mutational landscape of receptor guanylyl cyclase C: Functional analysis and disease‐related mutations

“…Many structural features may be conserved between Src kinases and KHD of GC‐C, 44 including Lys516 which was shown to be important for binding ATP in GC‐C, and which interacts with the β‐phosphate of ATP in kinases of known structure 36,43,45 . Interestingly, the KHD lacks the HRD motif, critical for catalysis by protein kinases, 36 and instead contains the HGR motif.…”

“…Sequence alignment indicates that the His and Gly are highly conserved across the KHD of all rGCs (Figure 3b), with Arg being replaced by either Ser or Asn in some members 46 . We have recently reviewed functional and structural aspects of the KHD of GC‐C in the context of other receptor GCs, kinases, and pseudokinases, to which the reader is referred 45 …”