The EF-hand Ca2+-binding Protein p22 Associates with Microtubules in an N-Myristoylation–dependent Manner

Proteins containing the EF-hand Ca2+-binding motif, such as calmodulin and calcineurin B, function as regulators of various cellular processes. Here we focus on p22, an N-myristoylated, widely expressed EF-hand Ca2+-binding protein conserved throughout evolution, which was shown previously to be required for membrane traffic. Immunofluorescence studies show that p22 distributes along microtubules during interphase and mitosis in various cell lines. Moreover, we report that p22 associates with the microtubule cytoskeleton indirectly via a cytosolic microtubule-binding factor. Gel filtration studies indicate that the p22–microtubule-binding activity behaves as a 70- to 30-kDa globular protein. Our results indicate that p22 associates with microtubules via a novel N-myristoylation–dependent mechanism that does not involve classic microtubule-associated proteins and motor proteins. The association of p22 with microtubules requires the N-myristoylation of p22 but does not involve p22’s Ca2+-binding activity, suggesting that the p22–microtubule association and the role of p22 in membrane traffic are functionally related, because N-myristoylation is required for both events. Therefore, p22 is an excellent candidate for a protein that can mediate interactions between the microtubule cytoskeleton and membrane traffic.

Behavioral inferences from the Skhul/Qafzeh early modern human hand remains

Two groups of humans are found in the Near East ≈100,000 years ago, the late archaic Neanderthals and the early modern Skhul/Qafzeh humans. Observations that Neanderthals were more heavily muscled, had stronger upper-limb bones, and possessed unusual shapes and orientations of some upper-limb joint complexes relative to the Skhul/Qafzeh hominids, have led some researchers to conclude that significant between-group upper-limb-related behavioral differences must have been present, despite the association of the two groups with similar Middle Paleolithic archeological complexes. A three-dimensional morphometric analysis of the hand remains of the Skhul/Qafzeh hominids, Neanderthals, early and late Upper Paleolithic humans, and Holocene humans supports the dichotomy. The Skhul/Qafzeh carpometacarpal remains do not have any unique morphologies relative to the other fossil samples remains examined. However, in the functionally significant metacarpal 1 and 3 bases they resemble Upper Paleolithic humans, not Neanderthals. Furthermore, the Skhul/Qafzeh sample differs significantly from the Neanderthals in many other aspects of hand functional anatomy. Given the correlations between changes in tool technologies and functional adaptations seen in the hands of Upper Paleolithic humans, it is concluded that the Skhul/Qafzeh hand remains were adapted to Upper Paleolithic-like manipulative repertoires. These results support the inference of significant behavioral differences between Neanderthals and the Skhul/Qafzeh hominids and indicate that a significant shift in human manipulative behaviors was associated with the earliest stages of the emergence of modern humans.

Role of essential light chain EF hand domains in calcium binding and regulation of scallop myosin.

The specific Ca2+ binding site that triggers contraction of molluscan muscle requires the presence of an essential light chain (ELC) from a Ca2+ binding myosin. Of the four EF hand-like domains in molluscan ELCs, only domain III has an amino acid sequence predicted to be capable of binding Ca2+. In this report, we have used mutant ELCs to locate the Ca2+ binding site in scallop myosin and to probe the role of the ELC in regulation. Point mutations in domain III of scallop ELC have no effect on Ca2+ binding. Interestingly, scallop and rat cardiac ELC chimeras support Ca2+ binding only if domain I is scallop. These results are nevertheless in agreement with structural studies on a proteolytic fragment of scallop myosin, the regulatory domain. Furthermore, Ca2+ sensitivity of the scallop myosin ATPase requires scallop ELC domain I: ELCs containing cardiac domain I convert scallop myosin to an unregulated molecule whose activity is no longer repressed in the absence of Ca2+. Despite its unusual EF hand domain sequence, our data indicate that the unique and required contribution of molluscan ELCs to Ca2+ binding and regulation of molluscan myosins resides exclusively in domain I.