reported recently, simulations using NAMD suggest now a simple and elegant answer: the finger proteins bundle in groups of 2 - 6 and form a brush, filling with its bristles the nuclear pores. The bristles are bundles of finger proteins and have two key properties: (i) on their surface they are dotted with spots of amino acid pairs, phenylalanine and glycine, that are known to interact favorably with transport receptors (see the Aug 2007 highlight, the Feb 2007 highlight, and the Jan 2006 highlight); (ii) the bristles are also interconnected, namely where finger proteins change from one bundle to another bundle, which they do with some frequency. It appears then that the bristles of the nuclear pore filter form an energetically favorable environment for transport receptors and that the latter can tear a finger protein readily away from a bundle to form a wider space for passage. More information here.
Transport-related structures and processes of the nuclear pore complex studied through molecular dynamics. Lingling Miao and Klaus Schulten. Structure, 17:449-459, 2009.
Lingling Miao and Klaus Schulten. Probing a structural model of the nuclear pore complex channel through molecular dynamics. Biophysical Journal, 2010. In press.